6 tablespoons extra-virgin olive oil, divided
2 cups finely onions
2 garlic cloves, minced
2 cups seeded and diced tomatoes
¼ cup dry white wine
3 to 4 fresh basil leaves, chopped
1 1/2 tablespoons capers, rinsed, drained
2 to 4 ahi tuna steaks, each about 1 inch thick)
Salt and pepper
Heat 3 tablespoons extra-virgin olive oil in heavy large skillet over medium heat. Add onions; sauté until tender, about 5 minutes. Add garlic; sauté 30 seconds, stirring constantly. Stir in tomatoes, wine and capers. Simmer uncovered until mixture thickens, stirring occasionally, about 5 minutes. Season with some salt and pepper. Stir in fresh basil.
Meanwhile, heat remaining 3 tablespoons oil in another heavy large skillet over medium heat. Sprinkle fish with salt and pepper. Add fish to skillet and cook until light brown at edges but pink in center, about 3 minutes per side. Serve fish immediately with tomato sauce over the top.