Why pesto and swordfish belong together
Pesto grilled swordfish works because swordfish is dense enough to hold its shape over high heat and mild enough to let basil, garlic, and pine nuts shine without fighting for attention. The pesto acts as both a marinade and a crust — it seasons the fish as it sits, then chars slightly on the grill to create a textured, flavorful surface. Fresh mozzarella melted on top in the last minute adds richness and a cool contrast to the heat of the grill.
This is not a delicate dish. Swordfish steaks are forgiving. They won't dry out the way a thin fillet would, and they won't fall apart if you move them on the grill. That makes this recipe good for a first time grilling fish, or for feeding a crowd where timing matters.
Key Takeaways
- Swordfish steaks should be cut one and a quarter to one and a half inches thick so they cook through without drying out over direct heat.
- Make pesto by hand or in a food processor, but do not over-blend — you want visible basil leaves and pine nut pieces, not a paste.
- Coat the fish with pesto and let it sit for 15 to 30 minutes before grilling so the flavors penetrate the flesh.
- Grill over medium-high heat for three to four minutes per side, then top with fresh mozzarella and cover to melt it in the last minute.
- Swordfish is done when it flakes easily at the thickest part and has lost its translucent look, not when it is bone-dry.
Choosing and preparing your swordfish steaks
Ask your fishmonger for steaks cut from the center of the loin, one and a quarter to one and a half inches thick. This thickness is the difference between a steak that stays moist inside and one that dries out. Thinner cuts cook too fast; thicker ones won't cook through before the outside chars.
Rinse the steaks under cold water and pat them completely dry with paper towels. Moisture on the surface will steam instead of sear, and you lose the crust that holds the pesto in place. If your steaks have a thin skin on one side, you can leave it or remove it — it will not hurt the dish either way, but removing it gives you more surface for pesto to cling to.
Making pesto that holds up to heat
Tear fresh basil leaves by hand rather than cutting them with a knife, which bruises the leaves and darkens them. You want about two cups of packed basil, one-third cup of pine nuts, three or four garlic cloves, half a cup of good olive oil, and half a cup of grated Parmigiano-Reggiano. Salt and pepper to taste.
If you use a food processor, pulse the basil, garlic, and pine nuts together first until they are broken into small pieces but still visible. Add the cheese and pulse once more. Drizzle in the olive oil while pulsing, just until the pesto comes together. If you make it by hand with a mortar and pestle, grind the garlic and pine nuts first, then add basil a handful at a time, grinding gently until you have a rough paste. Stir in the cheese and oil at the end.
The pesto should look chunky and loose, not smooth. Overworked pesto turns dark and bitter from the basil oils breaking down. You are making a coating, not a sauce.
Marinating and seasoning the fish
Spread a thin layer of pesto on both sides of each swordfish steak, using about a tablespoon per side. Do not be shy — the pesto will char and concentrate on the grill. Let the steaks sit at room temperature for 15 to 30 minutes. This gives the salt in the pesto time to draw moisture from the fish and season it all the way through, not just on the surface.
If you are grilling more than two hours later, cover the steaks and refrigerate them, then pull them out 20 minutes before you light the grill so they return to room temperature. Cold fish takes longer to cook and will not develop a proper crust.
Grilling technique for even cooking
Heat your grill to medium-high — you should be able to hold your hand six inches above the grate for only three or four seconds before the heat forces you to pull away. Oil the grate well with a high-heat oil like grapeseed or avocado oil on a folded paper towel held with tongs. This prevents sticking and helps the pesto crust form.
Place the steaks on the grill perpendicular to the grates, not parallel. This gives you cleaner grill marks and makes it easier to move the fish without it rolling. Grill for three to four minutes without moving them. You are looking for the pesto to darken and char slightly at the edges, and for the flesh to turn opaque about halfway up the side of the steak.
Flip once, using a wide metal spatula and a gentle hand. Grill the second side for another three to four minutes. The steak is done when a fork inserted at the thickest part flakes the flesh easily and the color has changed from translucent to opaque all the way through. If you have a meat thermometer, swordfish is done at 140°F.
Adding mozzarella and finishing
In the last minute of cooking, tear a small handful of fresh mozzarella into pieces and scatter it over the top of each steak. If your grill has a cover, close it. If not, tent the steaks loosely with foil. The residual heat will soften the mozzarella without cooking it hard. You want it melted and creamy, not browned.
Transfer the steaks to a warm plate and let them rest for two minutes. This allows the juices to redistribute through the flesh. Serve with lemon wedges and a simple salad of arugula dressed with olive oil and salt.
What to do if something goes wrong
If the pesto is charring too fast and the fish is still translucent inside, move the steaks to a cooler part of the grill or lower the heat. You can also tent them loosely with foil to slow the browning while the inside finishes cooking.
If the fish is sticking to the grill, do not force it. Let it sit for another 30 seconds — it will release when the crust has formed enough. If it still sticks, your grate was not oiled well enough; oil it again and try the next steak.
If you have overcooked the fish and it is dry, the mozzarella will help mask it slightly, but the lesson is to pull it off the grill a minute earlier next time. Swordfish continues to cook for a minute or two after you remove it from heat.
Frequently Asked Questions
Can I make the pesto ahead of time?
Yes. Pesto keeps in the refrigerator for up to three days in an airtight container, or you can freeze it for up to three months. If you freeze it, thaw it in the refrigerator overnight. The texture will be slightly looser after thawing, but the flavor is the same. Stir it well before using.
What if I don't have pine nuts?
Walnuts or almonds work in a pinch, though they will give you a slightly earthier flavor. Use the same amount. Toast them lightly in a dry pan first to bring out their flavor. Sunflower seeds are another option if you have a nut allergy.
Can I use a grill pan instead of an outdoor grill?
Yes. Heat a cast-iron grill pan or heavy skillet over medium-high heat until it is very hot. Oil it well, then cook the steaks for three to four minutes per side, the same as you would on an outdoor grill. You will get less dramatic grill marks, but the cooking time and doneness are the same.
How much mozzarella should I use per steak?
About one ounce, or a small handful torn into pieces. Too much will overwhelm the pesto; too little will barely melt. One ounce is roughly the size of a golf ball before you tear it.
Is swordfish sustainable to eat?
Swordfish populations vary by region and fishing method. Atlantic swordfish is considered sustainable by most standards. Ask your fishmonger where the fish came from and how it was caught. Harpoon-caught swordfish is generally considered the most sustainable option.