Cook penne in a large pot according to package directions. Drain and set aside,
In the same large pot cook Italian sausage until ¾ the way cooked. Remove from pot and cut into bite-size slices. In the same pan add olive oil, bell peppers, and onion.
Saute vegetables until tender then add sausage back to the pot. Add marinara sauce and cooked pasta to the pot. Cover and allow to cook on low for 4-5 minutes until everything is warm and well combined.