Preheat oven to 450°.
Heat a large nonstick skillet coated with cooking spray over medium-high heat. Add sliced onion and green bell pepper strips, and sauté 6 minutes or until tender.
Remove casings from sausage. Add sausage to pan, and cook 5 minutes or until lightly browned, stirring to crumble. Add crushed red pepper and diced tomatoes, and cook 5 minutes or until mixture thickens.
Spread sausage mixture evenly over cut sides of bread, and sprinkle evenly with cheese. Place bread halves on a baking sheet. Bake at 450° for 5 minutes or until cheese melts. Cut each pizza in half.