Add beef and onion to a large skiller over medium heat. Cook, stirring to break up lumps, until beef is browned, about 10 minutes. Drain excess fat.

Add green pepper and garlic; cook, stirring, until softened, 2-3 minutes. Add 1 cup water and bring to a boil, scraping up browned bits from bottom of skillet.

Stir in ketchup, brown sugar, mustard, salt, pepper, and Worcestershire sauce. Add remaining 1 cup of water and bring to a simmer. Reduce heat to low and continue simmering, uncovered, until liquid has evaporated and mixture thickens, about 40 minutes. Stir occasionally.

Stir in cayenne (if desired). Serve on buns with pickle slices!