Season tuna steak with salt and pepper and rub with garlic oil. Place on hot grill and cook to desired temp. Rub all veggies with garlic oil. Grill until tender. Season with pepper and sprinkle with balsamic vinegar. Sauce: Heat olive oil in 1 quart sauce pot. Add onions and saute onions until lightly browned. Add yellow peppers and time and sweat in olive oil 1 minute. Add stock and simmer covered until peppers are soft. Remove to blender and puree. Adjust seasoning and keepwarm. Spoon sauce