Combine vinegar, ⅓ cup olive oil, garlic, bay leaves, 1 teaspoon salt, pepper, and parsley in a zip-top plastic bag. Add tuna steaks, seal, and marinate 2 to 3 hours.
Saute onions until slightly soft. Sprinkle with 1 teaspoon salt. Add red peppers; cook until peppers are tender and onions are golden. Add Portuguese allspice and set aside; keep warm.
Remove tuna steaks from marinade and pat dry. In a separate skillet over medium-high heat, sear tuna in 2 tablespoons olive oil, 2 to 3 minutes on each side. Remove tuna from pan; keep warm. Add marinade to pan along with tomato, stirring until hot and slightly thick, about 3 to 5 minutes. Pour over tuna steaks. Place onion-pepper mixture on the side or on top of tuna. Serve with rice or boiled potatoes.