Heat garlic oil in a nonstick skillet over a medium-low heat, and then add sliced onions, stirring occasionally until the onions turn translucent.
While onions cook, generously apply salt and pepper to the tuna.
Remove the onions from the pan and raise heat to medium high and sear the tuna for about 2 minutes on each side.
While the tuna sears mix 6 ounces sweet chili sauce, with 2 ounces of dry white cooking wine and 2 ounces red wine vinegar.
Turn heat to low and return the onions to the pan with your mixture of wine and sweet chili sauce.
Cover the skillet to cook for about 5 more minutes.
Remove the tuna and then pour the desired amount of sauce over your steaks.