In a skillet on medium heat, cook down the ground beef. Once it starts to brown toss in the diced onion. Cook until the meat is browned and cooked through.
Add in the diced bell pepper, tomato sauce, tomato paste, worcestershire sauce, smashes garlic, brown sugar, salt, ground mustard and red pepper flakes. Stir together and then bring to a simmer.
Turn to low heat and simmer for 15-20 minutes.
Serve on buns and top with coleslaw if you desire to add a nice fresh crunch.