Add the olive oil to a large skillet on the stove over medium high heat. Add the onion and bell peppers, cook for 3-4 minutes. Add the ground beef and cook through.
Once cooked through, drain any grease from the meat, then add it to a crock pot.
Add the ketchup, mustard, brown sugar, garlic powder, chili powder, salt and pepper to the crock pot and stir well.
Cook on high for 3 hours or low for 6 hours.
Serve on slider buns or Hawaiian rolls and top with crispy onions.