Heat oven to 350°F. Grease a 3-quart dish or use an oven-safe Dutch oven.
Cook bacon in a large Dutch oven over medium heat until crisp, 6–8 minutes. Drain on paper towels.
Brown ground beef in the bacon drippings until no pink remains, 5–7 minutes. Drain excess fat.
Sauté onion and bell pepper until softened, 4–5 minutes. Stir in garlic for 30 seconds.
Add pork and beans, kidney beans, and pinto beans. Stir to combine.
Whisk barbecue sauce, ketchup, brown sugar, molasses, mustard, vinegar, Worcestershire, paprika, and chili powder.
Pour sauce into the pot. Season with salt and pepper. Mix well.
Fold bacon back in. Transfer to the dish if your pot isn’t oven-safe.
Bake uncovered until bubbly and thick, about 35 minutes. Rest 10 minutes before serving.