01 - Heat a large skillet over medium heat. Brown the ground beef, breaking it apart until fully cooked, about 6 to 8 minutes. Drain excess fat if necessary.
02 - Add the chopped onion, green bell pepper, and minced garlic to the beef. Cook until softened, approximately 4 to 5 minutes.
03 - Stir in tomato sauce, ketchup, Worcestershire sauce, brown sugar, yellow mustard, smoked paprika, salt, and black pepper. Mix thoroughly and bring to a simmer.
04 - Reduce heat to low and let the mixture simmer uncovered for 10 to 12 minutes, stirring occasionally until thickened.
05 - Preheat a small skillet or grill pan over medium heat. Spread softened butter on the cut sides of the hamburger buns. Toast buttered sides down until golden brown, about 2 minutes.
06 - Spoon the beef mixture onto the bottom halves of the toasted buns. Cover with the top halves and serve immediately while hot.