Lay tuna steaks flat in a large saute pan. Season with 2 teaspoons of salt, pepper and granulated garlic to taste. Pour enough water to cover fish by 1/4 inch then add vinegar. Bring liquid to a boil over medium-high heat, shifting fish from time to time to keep from sticking to the bottom of pan. When liquid is boiling, partially cover pan and adjust heat to simmer, maintaining a steady but gentle bubbling. Cook 15 minutes or until steaks are cooked through. Test by cutting into one steak to ensure meat is thoroughly cooked. Remove steak to a wire rack with a wide spatula and pat dry using paper towels. Allow to dry thoroughly and cool approximately 1 hour, turning fish once after 30 minutes. Set aside. While fish is cooling, place saute pan over medium-high heat. Add olive oil, red onion slices, garlic, bay leaves and red cayenne peppers. Bring oil to 190 degrees F and poach vegetables, stirring occasionally, until onions are wilted and seasonings beginning to impart flavor, 10-15 minutes. Do not heat above 190 degrees F, otherwise onions will overcook or fry. Pour oil and seasoning from skillet into a glass bowl and allow to cool 30 minutes. When fish is dry, cut steaks into 1-inch cubes that will fit nicely into the jars. Using a pair of tongs, evenly distribute fish pieces, onion slices, 2 garlic cloves, 1 bay leaf, 1 cayenne pepper and a pinch of peppercorns into each jar. Ladle an equal amount of olive oil into each jar, making sure to cover fish by 1/4 inch. Tap repeatedly on sides of jars to shake loose any air bubbles. Let containers sit 15 minutes for all bubbles rise to surface. Fill jars to 1/8 inch to the top with additional olive oil. Cover jars with lids, place in a large canning pot then cover jars with hot water by 3 inches. Bring to a low boil, cover and cook 45 minutes to cure. Remove from hot water, place upside-down onto kitchen towels and allow to cool 12 hours. Place in refrigerator and allow to marinate 1 week prior to opening. Fish may be served over salad greens or used chopped along with mayonnaise and seasoning to create the ultimate tuna sandwich.