Ingredients:

  Amount  Measure       Ingredient -- Preparation Method
--------  ------------  --------------------------------
   1      tablespoon    olive oil
   2      cups          chopped onion
     1/2  cup           red wine vinegar
     1/4  teaspoon      salt -- divided
     1/4  teaspoon      pepper -- divided
     1/2  cup           all-purpose flour
   8                    tuna steaks -- (4-ounce)
                        (3/4 inch thick)
   2      teaspoons     olive oil
                        mint sprigs -- (optional)

Preparation:

Heat 1 tablespoon oil in a large nonstick skillet over medium-high heat. Add onion, and sauté 5 minutes or until lightly browned. Add vinegar, 1/8 teaspoon salt, and 1/8 teaspoon pepper, and cook for 2 minutes or until most of liquid evaporates. Remove the onion mixture from skillet; set aside, and keep warm. Wipe skillet clean with a paper towel. Combine the flour and remaining salt and pepper in a shallow dish, and stir well. Dredge tuna in flour mixture. Heat 2 teaspoons oil in skillet over medium heat. Add tuna, and cook for 2 minutes on each side until tuna is medium-rare or desired degree of doneness.