Prepare pasta according to recipe (see meal.) Chop onion and olives; drain tuna (or rinse and drain to decrease the sodium if you cannot get low sodium tuna.) In a nonstick saucepan, heat oil over medium heat and sauté onion until translucent, about 2-3 minutes. With a fork, flake tuna into saucepan and add olives, canned tomatoes with liquid, and pepper flakes. Partially cover saucepan, reduce heat to low and simmer for about 15-20 minutes, stirring occasionally, until most of the liquid has evaporated. Add cooked pasta to the sauce, heat through, 1-2 minutes, and serve.