Slice the sausages diagonally. Thinly slice the onion, cut the bell peppers into thin strips, and finely chop the garlic.
Cook the spaghetti in plenty of boiling water for 1 minute longer than the package directions.
Heat the olive oil in a pan over medium heat. Cook the sausages until nicely browned.
Add the onion, bell peppers, and garlic. Stir-fry briefly.
Push the ingredients to one side of the pan. Add the ketchup, Worcestershire sauce, and sugar to the empty space. Cook over medium heat for 1–2 minutes to slightly reduce the sauce.
Drain the spaghetti and add it to the pan. Stir-fry well over medium heat until the pasta is fully coated in the sauce.
