Preheat oven to 350°F (175°C). Grease a loaf pan or line with parchment paper.
In a large mixing bowl, combine ground beef, onion, bell pepper, crushed Ritz crackers, eggs, milk, salt, pepper, and ½ cup ketchup. Mix until just combined—do not overmix.
Transfer the mixture into the prepared loaf pan and shape evenly.
In a small bowl, whisk together ½ cup ketchup, brown sugar, and mustard. Spread this glaze evenly over the top of the meatloaf.
Bake uncovered for 55–60 minutes, or until internal temperature reaches 160°F (71°C).
Let rest for 10 minutes before slicing and serving.