For the tuna spaghetti with lemon, first cook the pasta in salted water until al dente. Meanwhile, sauté the onions, finely chopped, in a little oil (from the tuna can) until translucent. Deglaze the onions with the juice of the lemon and add the tuna with the remaining oil and season.
When the pasta is cooked, remove it directly from the water and add it to the tuna mixture. If it is a little too dry, add a little pasta water by the ladle if necessary. Now add the black olives and serve the tuna spaghetti with lemon immediately!