- In a large skillet, heat the olive oil over medium heat. Add the ground beef and cook until browned, breaking it up with a spoon as it cooks, about 5-6 minutes. Drain excess fat.
- Add the chopped onion, green bell pepper, and garlic to the skillet with the beef. Cook for another 2-4 minutes, until the vegetables are softened.
- Transfer beef and vegetable mixture to a slow cooker.
- In the slow cooker, add the tomato sauce, ketchup, tomato paste, Worcestershire sauce, Dijon mustard, brown sugar, smoked paprika, chili powder, salt, and pepper. Stir everything well to combine.
- Cover and cook on low for 4-6 hours, or on high for 2-3 hours, stirring occasionally.
- Once the Sloppy Joes are fully cooked and the sauce has thickened, serve the mixture on toasted hamburger buns. Add optional toppings like pickles, cheese, or coleslaw if desired.