01 - Heat a large skillet over medium-high heat. Add the ground beef and cook, breaking it apart with a spatula, until browned and no longer pink, approximately 5 minutes. Drain excess fat if necessary.
02 - Add the chopped onion, bell pepper, and garlic to the skillet with the beef. Sauté for 3 to 4 minutes until the vegetables are softened and fragrant.
03 - Pour in the tomato sauce, tomato paste, ketchup, Worcestershire sauce, brown sugar, mustard, smoked paprika, salt, black pepper, and red pepper flakes. Stir thoroughly to combine all ingredients.
04 - Reduce heat to low and let the mixture simmer uncovered for 8 to 10 minutes, stirring occasionally, until the sauce has thickened to a hearty consistency.
05 - While the meat mixture simmers, butter the cut sides of the hamburger buns. Toast them on a skillet or griddle until golden and crisp.
06 - Spoon the hot Sloppy Joe mixture generously onto the bottom half of each toasted bun. Place the top half over the filling and serve immediately.