Heat olive oil in a large skillet over medium heat.
Add ground beef and cook until browned, about 3-5 minutes, breaking up the meat with a spoon.
Stir in onion and bell pepper, and cook until tender, about 3 minutes.
Add garlic and cook for about 1 minute, stirring frequently.
Stir in ketchup, brown sugar, mustard, Worcestershire sauce, and chili powder; season with salt and pepper.
Reduce heat and simmer until the sauce has thickened, about 5 minutes.
Spoon the sloppy joe mixture onto the toasted buns and serve immediately.