Heat some olive oil in a medium size skillet and sauté the chopped onion until it is soft, but not browned. Add the garlic and continue to cook.
Add the chopped tomatoes and wine, and cook over medium heat for about 5 to 10 minutes, or until the desired consistency is reached. Add the green olives and fresh lemon juice to warm through.
Taste the sauce and season with plenty of salt and freshly ground pepper, and finish with more high-quality extra-virgin olive oil and any fresh herbs you have on hand. Keep warm.
Sear the Tuna
While the sauce finishes cooking, heat a cast-iron skillet over high heat with a drizzle of canola oil until it starts to smoke.
Pat the tuna steaks dry with a paper towel, then season with salt and plenty of freshly ground pepper. Gently push the seasoning into the tuna to help it stick while it cooks.
Sear the tuna in the smoking hot skillet for about 1 minute per side for rare.
Slice the tuna steaks against the grain with a very sharp knife and serve over the fresh tomato and olive sauce. Drizzle with a little more extra-virgin olive oil and a sprinkle of sea salt on the sliced tuna.
Canned whole tomatoes can be used if ripe tomatoes aren't available. Use the tomatoes only and not the water from the can.