2 tuna steaks (such as albacore or yellowfin; each about 6 oz. and 1 in. thick)
Salt and pepper
1 tablespoon olive oil
1 onion (8 oz.), peeled, halved lengthwise, and thinly sliced
1 can (14 1/2 oz.) crushed tomatoes in purée
1/2 cup dry red wine
3 tablespoons balsamic vinegar
1 tablespoon drained capers
1 teaspoon dried oregano
How to Make It
Rinse tuna steaks and pat dry. Sprinkle lightly all over with salt and pepper. Pour oil into a 10- to 12-inch nonstick frying pan over high heat. When hot, add onion and stir frequently until limp, about 5 minutes.
Push onion to side of pan and add tuna steaks. Cook, turning once, just until browned on both sides, 3 to 4 minutes total. Stir in crushed tomatoes, wine, vinegar, capers, and oregano.
Reduce heat to maintain a simmer, cover, and cook until tuna is no longer pink in the center (cut to test), about 15 minutes. Transfer tuna to plates and top equally with sauce.