In a large skillet over medium-high heat, cook the chopped bacon until crispy. Remove the bacon with a slotted spoon and set aside. Add the ground beef and diced onion to the skillet with the bacon fat. Cook until the beef is browned and the onion is tender. Drain any excess grease.

Transfer the cooked beef and onion mixture to a 6-quart or larger slow cooker. Add the crispy bacon, undrained pinto beans, undrained kidney beans, and undrained great northern beans.

Pour the BBQ sauce, brown sugar, apple cider vinegar, Worcestershire sauce, garlic powder, and mustard powder into the slow cooker. Stir all ingredients together until everything is well combined.

Cover the slow cooker and cook on LOW for 6-8 hours or on HIGH for 3-4 hours. The beans are done when the sauce is thick and bubbly.

Let the cowboy beans rest for 15-20 minutes before serving to allow the sauce to thicken slightly. Serve warm.