Preheat oven to 300°F (150°C).

Brown ground beef in a large skillet over medium-high heat, breaking it up into small pieces as it cooks, until it is no longer pink, about 5-7 minutes.

Add onion and bell pepper to the skillet and cook until the vegetables are softened, about 5 minutes.

Stir in tomato sauce, Worcestershire sauce, and chili powder, and bring the mixture to a simmer.

Reduce heat to low and let the mixture cook, stirring occasionally, until the flavors have melded together and the sauce has thickened, about 20-25 minutes.

Season the mixture with salt and pepper to taste.

Split hamburger buns in half and toast them in the oven until they are lightly browned, about 5 minutes.

Spoon the sloppy joe mixture onto the toasted buns and serve immediately.