Steps

1. Heat the olive oil in a large sauté pan over medium-high heat. Add the fish steaks in a single layer and sprinkle the onion and parsley over and around them. Sear the fish for about 1 minute per side so the flesh whitens and tightens.
2. Turn the heat down to medium-low. Scatter the basil, garlic and 3 tablespoons of the wine around the fish. Sprinkle lightly with salt and pepper. Cook for 2 or 3 minutes more per side, or until still rare enough to give a little when pressed. Transfer the tuna steaks onto a heated platter and hold warm.
3. Return the sauté pan to the stovetop and turn the heat up to high. Add the remaining wine and boil for about 30 seconds, scraping up any brown bits in the pan. Stir in the tomato and olives and cook, stirring, for about 20 seconds.
4. Place the tuna steaks onto serving platters and spoon the tomato sauce over the tuna. Garnish with more basil and serve.