Remove casings from sausage. Cook sausage in a Dutch oven over medium high heat until browned, stirring to crumble. Add bell pepper and onion; cook 3 minutes or until tender, stirring occasionally. Add mushrooms and garlic; cook 5 minutes or until vegetables are tender, stirring occasionally. Stir in water, sundried tomatoes, and crushed tomatoes; bring to a boil. Cover, reduce heat, and simmer 10 minutes. Add Italian seasoning and black pepper; simmer 5 minutes.
Meanwhile, heat a large nonstick skillet over medium-high heat. Coat polenta slices with cooking spray; add to pan. Cook 4 to 5 minutes on each side or until browned.
Place 2 polenta slices on each of 4 plates; top each with 3/4 cup sauce and 3/4 teaspoon cheese.