Source: La Fontanella - Phoenix, Arizona (originally from Chicago, Illinois)
4 (1-inch) slices of Ahi tuna
2 large onions
1/2 cup red wine vinegar
1/2 cup white wine
1/2 cup olive oil
Extra virgin olive oil
Season tuna with salt and pepper. Slice onion thinly into matchsticks.
Heat large skillet; add oil and onions. Sweat and cook until caramelized golden. Add vinegar and wine. Boil to evaporate alcohol; add tuna. Cook 3 minutes on each side. Keep fish moist, adding water if necessary.