In a large pot with boiling salted water, cook pasta until al dente. Drain.
Meanwhile, in a large skillet over medium-high heat melt butter, add onion and garlic and cook for 2 minutes. Add sausage and continue cooking, stirring occasionally, about 6 minutes, until sausage is no longer pink.
Reduce heat to medium-low. Add peas, green pepper, chopped tomato, Parmesan cheese, fresh parsley, lemon juice and drained pasta to the large skillet. Cook until heated through, about 2 to 3 minutes.