Melt butter in a large pot over medium heat; cook and stir green bell peppers, onion, and garlic in the hot butter until vegetables are slightly soft, 2 minutes. Stir sausage and ground beef into bell pepper mixture; cook until meat is crumbly and browned, stirring often, 10 to 12 minutes. Drain grease. Season mixture with salt, black pepper, oregano, and garlic powder.
Mix diced tomatoes, rice, tomato paste, and Worcestershire sauce into meat mixture and bring to a simmer; cook until heated through, about 5 minutes, stirring occasionally. Pour mixture into a large baking dish.
Whisk tomato soup with water in a bowl until smooth; pour soup over meat mixture. Spread Cheddar cheese over casserole.
Bake in the preheated oven until casserole is heated through and Cheddar cheese is browned and bubbling, about 30 minutes.