Cook pasta in large pot of boiling water, drain.
Meanwhile, heat oil in large skillet over high heat. Add onion; cook until browned, 2 minutes. Add chili pepper if using, garlic and meat; cook, breaking up meat, until it loses its raw look, about 3 minutes.
Add tomatoes, tomato paste, salt and pepper; bring to boiling. Lower heat; simmer 5 minutes. Adjust salt and pepper if necessary. Stir in parsley. Remove chili pepper.
Toss cooked pasta with sauce.