Combine the soy sauce, orange juice, vinegar, brown sugar, orange peel, garlic, and hot pepper sauce in a dish. Add the tuna. Cover and set aside for 15 minutes. Light grill or broiler.
When the coals are ash covered or the gas grill is hot, place the tuna on grill (or 6 inches beneath broiler). Dip the potatoes, tomatoes, peppers, and onion into the marinade and arrange, cut side down, on grill. Cover and cook 7 minutes. Turn over the fish and vegetables. Discard the marinade.
Cover and cook 5 to 7 minutes more or until the tuna is opaque and the vegetables are fork-tender.
Combine the romaine and basil on a platter. Sprinkle with the olive oil, lemon juice, salt, and pepper. Toss. Arrange grilled items on top. Serve.