Gather the ingredients. Prepare all ingredients, chop the bacon and onions, and rinse and drain the kidney beans and lima beans.
Cook the ground beef and bacon. Heat a large skillet over medium-high heat. Add the ground beef and chopped bacon. Cook for 7–10 minutes, stirring frequently and breaking the beef into small crumbles, until the ground beef is browned.
Transfer to the slow cooker. Add the cooked ground beef and bacon to the slow cooker.
Add the beans and onions. Stir in the chopped onions, baked beans with pork, rinsed kidney beans, and drained lima beans.
Mix in the sauce ingredients. Add the ketchup, brown sugar, and prepared mustard. Stir thoroughly until the beans and meat are evenly coated with the sauce.
Slow cook. Cover the slow cooker and cook on Low for at least 3 hours, until the mixture is hot, bubbling, and thickened.
Stir and serve. Gently stir the cowboy beans before serving. Spoon into bowls and serve warm as a hearty main dish or alongside your favorite barbecue foods.