Place all of the ingredients for the tuna balls in a food processor. Pulse until smooth paste forms. Add more oil if needed to help it stick together. Form into balls. Set aside.
Heat a few tablespoons of olive oil in a pan. Add the tuna balls and brown, turning once, for about 5-10 minutes. Remove to a paper towel-lined plate.
In the same pan, you cooked the tuna balls in, add the anchovy paste, onion, garlic, olive and capers and saute until the onions are translucent, about 5 minutes. Add the tomatoes and simmer 5 minutes.
Add the tuna balls back to the pan. Cook until heated through, about 5-10 minutes.
Serve on hot spaghetti.