Make the sloppy joes: Chop the onion and bell pepper. In a large oven-safe nonstick skillet over medium-high heat, cook the ground beef, onion, and green pepper until browned, about 6–8 minutes. Reduce the heat if the beef cooks too quickly. Stir in the ketchup, mustard, brown sugar, garlic, smoked paprika, salt, and pepper until combined.
1 pound ground beef, ¼ cup onion, ¼ cup green bell pepper, ¾ cup ketchup, 1 tablespoon yellow mustard, 1 tablespoon brown sugar, 1 teaspoon garlic, 1 teaspoon smoked paprika, ½ teaspoon salt, ¼ teaspoon black pepper