Heat oil and butter in a large skillet over medium-high heat. Add ground beef and cook for 4-5 minutes. Transfer to a colander to drain.
Now add bell pepper and onion to the same skillet and cook 3-4 minutes or until soft.
After that add garlic and cook for 1 minute or until fragrant. Add beef again to the skillet along with the tomato paste. Mix them well.
Add water, ketchup, mustard, brown sugar, chili powder, Worcestershire sauce, red pepper flakes, salt, and black pepper. Mix them well to combine.
Cook over medium heat for 12-15 minutes, until mixture, has thickened.
It’s ready. Turn off the heat and serve over toasted buns.