1. Preheat your oven to 400°F. Grease a 13×9-inch baking dish lightly with butter.
2. In a large skillet over medium heat, brown the ground beef until fully cooked. Drain excess fat.
3. Add the diced onion and green bell pepper to the skillet. Cook until the onion is translucent and the bell pepper is tender.
4. Stir in the brown sugar, Worcestershire sauce, dry mustard, garlic salt, tomato sauce, and ketchup. Allow the mixture to simmer for about 5 minutes.
5. In a medium bowl, mix the flour, baking powder, and salt.
6. Add milk, melted butter, and the egg to the flour mixture, stirring until a thick batter forms.
7. Stir in the shredded cheddar cheese until evenly distributed in the batter.
8. Pour the simmered beef mixture into the prepared baking dish. Dollop the cheese batter over the meat mixture, spreading evenly.
9. Bake in the preheated oven for 25-30 minutes or until the crust is golden brown.
10. Let the casserole cool slightly before serving.