Add ground beef, diced bell peppers, and diced onions to a large, deep skillet. Cook over medium heat until the beef is no longer pink and the vegetables begin to soften. Drain excess grease if necessary.
Stir in the minced garlic, mix well, and sauté for 3-5 minutes more.
Add the stuffing mix, tomatoes, Worcestershire sauce, Montreal grill seasoning, salt, pepper, paprika, 1 c. shredded cheese, butter, and beef stock. Stir well.
Cook over medium heat for 10-15 minutes, stirring occasionally.
Top the casserole with the remaining cheese, cover, and allow the cheese to melt.