Cook the meat and vegetables: In a large skillet over medium-high heat, add 1 pound of lean ground beef, 1/4 cup chopped onion, and 1/4 cup chopped red bell pepper. Cook, stirring occasionally, until the beef is browned and vegetables are tender, about 5-7 minutes. Drain excess liquids.
Add flavoring ingredients: Stir in 1/2 teaspoon garlic powder, 1 teaspoon prepared yellow mustard, 1/2 cup ketchup, 1/4 cup barbecue sauce, 3 teaspoons brown sugar, and 1/2 teaspoon Worcestershire sauce. Mix well until the beef and vegetables are coated in the sauce.
Simmer: Reduce the heat to low and allow the mixture to simmer for about 30 minutes, stirring occasionally. This allows the flavors to meld beautifully. Season with salt and ground black pepper to taste.
Prepare the buns: While the meat mixture simmers, toast your favorite hamburger buns. Spread a little butter on the cut sides and place them under the broiler until golden brown.
Assemble: Spoon a generous amount of the sloppy joe mixture onto the toasted buns. Serve immediately while hot and enjoy this delightful dish!