Posted: 11/13/2007 - Preheat the oven to 375°F. In a large skillet, heat the oil over medium-high heat. Add the ground beef, bell pepper, onion, and mushrooms, and cook for 6 to 8 minutes, stirring to crumble the beef, until no pink remains; drain excess liquid. Add the remaining ingredients except the cheese; mix well. Place in a 2-1/2-quart casserole dish, cover, and bake for 22 to 25 minutes. Remove the casserole from the oven, uncover, and top with the mozzarella cheese. Bake uncovered for 5 to 7 minutes, or until heated through and the cheese is melted.