Preheat the oven to 375°F. Line a baking tray with foil and lightly grease the surface.

In a large bowl combine salt, black pepper, chopped onion, chopped bell pepper, drained diced tomatoes, quick cooking oats, and the lightly beaten egg. Stir until the ingredients are evenly distributed.

Add ground beef and fold it in gently. Handle the meat as little as possible to avoid a dense loaf.

Shape the mixture into a compact, even mound about 8 inches long on the prepared tray.

In a small bowl, stir together ketchup, brown sugar, and mustard until smooth. Spread the glaze evenly over the top of the meatloaf.

Bake for about 1 hour, or until an instant-read thermometer inserted into the center reads 160°F. Remove the meatloaf and let it rest for 10 minutes before slicing.