Seared Tuna with Avocado and Salsa Verde

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.

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.