Cook pasta according to package directions; drain. Meanwhile, in large skillet cook sausage until browned and cooked through, about 10 minutes.

Remove; set aside. Drain off all but 1 tablespoon fat or add oil to make 1 tablespoon; heat until hot. Add mushrooms, green pepper and onion; cook, stirring occasionally, until tender, 5 to 7 minutes. Add reserved sausage and marinara sauce; cook until heated through, about 5 minutes. Ladle sauce over hot pasta.