• Fast

Ingredients

1. 2/3 cup lightly packed flat-leaf parsley leaves
2. 3 tablespoons drained capers
3. 1 clove garlic, smashed
4. 4 teaspoons lemon juice
5. 1 teaspoon anchovy paste
6. 1/2 teaspoon Dijon mustard
7. 3/4 teaspoon salt
8. 1/4 teaspoon fresh-ground black pepper
9. 1/2 cup plus 1 tablespoon olive oil
10. 4 tuna steaks, about 1 inch thick (about 2 pounds in all)
11. 1 avocado, cut into 1/2-inch chunks

Directions

1. Put the parsley, capers, garlic, lemon juice, anchovy paste, mustard, 1/2 teaspoon of the salt, and 1/8 teaspoon of the pepper into a food processor. Pulse to chop, six to eight times. With the machine running, add the 1/2 cup oil in a thin stream to make a coarse puree. Leave the sauce in the food processor and, if necessary, pulse to re-emulsify just before serving.
2. Heat a grill pan or heavy cast-iron pan over moderately high heat. Rub the tuna steaks all over with the 1 tablespoon oil. Sprinkle with the remaining 1/4 teaspoon salt and 1/8 teaspoon pepper. Cook the fish for 3 minutes. Turn and cook until done to your taste, 3 to 4 minutes longer for medium rare. To serve, top the tuna steaks with the avocado and drizzle with the sauce.

Notes

Fish Alternatives
Firm fish steaks, such as sturgeon, mako shark, and swordfish, all make excellent alternatives to the tuna. You'll want to cook them longer until just done, rather than medium rare.