Preheat your oven to 350°F (175°C).
In a large skillet, cook the diced bacon over medium heat until it is crispy. Remove the bacon with a slotted spoon and set it aside, leaving the bacon grease in the skillet.
Add the chopped onion and green bell pepper to the skillet and sauté them in the bacon grease until they are soft and translucent about 5 minutes.
Combine the pork and beans, kidney beans, black beans, barbecue sauce, brown sugar, yellow mustard, Worcestershire sauce, chilli powder, sautéed onions and bell peppers, and cooked bacon in a large mixing bowl. Mix everything thoroughly.
Pour the mixture into a 9×13-inch baking dish and smooth it out evenly. Cover the dish with aluminium foil and bake in the oven for 45 minutes. Remove the foil for the last 10 minutes of baking to allow the top to caramelize and thicken.