Chop the onions and fry them in oil until translucent, cut the pork belly into small cubes and add. Fry everything until the onions are melted.
Wash the tomatoes, cut them in half and add them. Cover and simmer the sugo on a low heat. Cook the spaghetti with a little salt in plenty of water (al dente), mix with the sauce and sprinkle with plenty of pecorino cheese.