1. In a large frying pan, over medium high heat, cook ground beef until brown. Drain the fat and discard.
2. Add onions, green pepper, and garlic. Sauté until vegetables begin to soften.
3. Add milk, brown sugar, chili powder, dry mustard, red pepper flakes, tomato paste Worcestershire, and ketchup . Stir to combine and simmer over medium low for 15-20 minutes, adding salt and pepper to taste.
4. To serve, slice buns in half and spoon meat mixture over each half of the bun