In a large mixing bowl, combine the ground beef, breadcrumbs, chopped onion, green bell pepper, minced garlic, beaten egg, milk, Worcestershire sauce, salt, and black pepper. Mix until well incorporated.
Gently fold in half of the shredded cheddar cheese into the meat mixture.
Press the meat mixture evenly into the bottom of a greased 9x13 inch baking dish.
Evenly distribute the canned diced tomatoes over the meat mixture.
Sprinkle the frozen mixed vegetables on top of the tomatoes.
Spread the ketchup evenly across the top of the casserole.
Top with the remaining shredded cheddar cheese, ensuring it covers the entire surface.
Bake in the preheated oven for 40-45 minutes, or until the meat is cooked through and the cheese is bubbly and golden.
Remove from the oven and let it cool slightly before slicing.
Notes
Serve slices of the casserole on individual plates, garnished with fresh parsley. Add a side salad for contrast and color.