Boil the spaghetti in salted water.
Finely chop the onion and garlic.
Heat olive oil in a pan and sauté the garlic and onion.
Add spicy tuna and tomato sauce to the pan and stir-fry.
Add the boiled spaghetti noodles to the pan and mix well with the sauce.
Season with salt and pepper, then serve on a plate.