For the swordfish and marinade: Whisk together the olive oil, white wine, lemon juice, tarragon, shallot and some salt and pepper in a container large enough to hold the fish. Add the swordfish and marinate, refrigerated, for about 1 hour, making sure the fish is coated and covered in the marinade.
For the tomatillo salsa: Add the tomatillos, onion, cilantro, olive oil, garlic, jalapeno, lime juice and some salt and pepper to a food processor and pulse to a chunky puree.
Heat a grill over medium-high heat.
Grill the swordfish until cooked through, 4 to 5 minutes per side. Rest the fish for 5 minutes, then cut into 1/4-inch slices or chunks.
For the tacos: Layer each tortilla with a couple slices of swordfish. Top with some tomatillo salsa, tomatoes, avocados and lettuce. Finish with a squeeze of lime juice.