Brown the ground beef in a large skillet over medium heat, breaking it up as it cooks. Drain excess fat.
Transfer the beef to the slow cooker. Add onion, bell pepper, and garlic. Stir to combine.
Whisk together tomato sauce, ketchup, tomato paste, brown sugar, Worcestershire, mustard, vinegar, chili powder, paprika, salt, pepper, and red pepper flakes.
Pour the sauce into the slow cooker and mix well to coat the beef and vegetables.
Cover and cook on LOW for about 5 hours, stirring once halfway through.
If you prefer a thicker mix, uncover for the last 20 minutes to let it reduce slightly.
Spoon onto toasted hamburger buns and serve warm.
Notes
Variation: Swap half the beef for ground turkey, or add 1 cup finely diced mushrooms to stretch the mixture. For a sweeter vibe, stir in 1–2 tablespoons of your favorite BBQ sauce. Leftovers keep 4 days refrigerated or freeze up to 3 months; reheat gently and splash in a little water if needed.This recipe is an original creation inspired by classic Easy Slow Cooker Sloppy Joes flavors. All ingredient ratios and instructions are independently developed.