Preheat the oven to 350 degrees. Place the ground beef in a mixing bowl and add the crushed Ritz crackers, milk, egg, onion, green bell pepper, salt, and black pepper.
Mix the ingredients with your hands or a fork just until combined. Avoid overmixing to keep the texture light.
Shape the mixture into a loaf and set it in a loaf pan or on a rimmed baking sheet lined with foil.
Spread the ketchup evenly over the top of the loaf.
Bake for 55 to 60 minutes until the internal temperature reaches 160 degrees. Remove from the oven and let the meatloaf rest for 5 minutes before slicing.