Either in skillet or oven, cook bacon. When done, drain fat and chop into small pieces and set aside.
In same skillet, brown ground beef, onions and pepper. When almost done, add in garlic and allow to cook for additional 2 minutes. Remove from stove and drain fat.
To the bottom of slow cooker, add in bacon, ground beef, peppers, onions and garlic. Add beans to top of meat mixture.
Add in ketchup, brown sugar, vinegar and yellow mustard and stir.