Step 1: Preheat your oven to 350°F (175°C).
Step 2: In a large Dutch oven or oven-safe pot, cook the diced bacon over medium heat until crispy. Remove the bacon with a slotted spoon and set aside, reserving about 2 tablespoons of bacon fat in the pot.
Step 3: Add the ground beef to the pot with the bacon fat. Cook over medium-high heat, breaking it up with a spoon, until browned. Drain any excess fat.
Step 4: Add the chopped onion and green bell pepper to the pot. Cook until softened, about 5-7 minutes. Stir in the minced garlic and cook for another minute until fragrant.
Step 5: Stir in the pork and beans (undrained), rinsed and drained kidney beans, and pinto beans into the pot with the beef and vegetables.
Step 6: Add the BBQ sauce, ketchup, molasses, brown sugar, yellow mustard, apple cider vinegar, liquid smoke (if using), smoked paprika, chili powder, and black pepper. Stir well to combine all ingredients.
Step 7: Bring the mixture to a gentle simmer on the stovetop. Once simmering, cover the pot and transfer it to the preheated oven. Bake for 60 minutes.
Step 8: After 60 minutes, remove the lid and stir the beans. Continue to bake uncovered for another 30 minutes, or until the sauce has thickened to your desired consistency and the top is slightly caramelized.
Step 9: Remove from the oven. Garnish with the reserved crispy bacon bits before serving. Let stand for 10-15 minutes before serving to allow the flavors to deepen.