1. Cook pasta according to package directions; drain and set aside.
2. Meanwhile, in a large skillet, heat 2 tablespoons oil over medium-high heat then add sausage, and cook 8 to 10 minutes, or until no longer pink in center. Remove to a bowl and cover with plastic wrap.
3. Add remaining 2 tablespoons oil to skillet. Add garlic, bell pepper, and onion, and cook 5 minutes, stirring occasionally. Stir in mushrooms, tomatoes, salt, and black pepper, and cook 7 to 10 more minutes, or until tomatoes have broken down.
4. Return sausage to skillet and cook 2 to 3 minutes, or until heated through. Serve over warm penne pasta.