Cut the bacon into 1-inch pieces and cook in a large skillet over medium heat, stirring occasionally, until the bacon has released about 1/4 cup of fat and the pieces are partially cooked but still slightly chewy (not fully crispy). Remove the bacon with a slotted spoon, leaving the rendered fat in the pan. I prefer to stop the bacon short of full crispness here because it will finish cooking in the oven and won't dry out. Reserve the cooked bacon for topping later.
In the same skillet with the bacon fat still in it, add the diced onion and green pepper over medium heat. Cook for about 5 minutes, stirring occasionally, until the vegetables are softened and fragrant. This step builds a flavorful foundation by allowing the aromatics to release their natural sugars and develop deeper flavor before combining with the beans.
Add the pork and beans, BBQ sauce, brown sugar, apple cider vinegar, Worcestershire sauce, smoked paprika, and mustard powder to the skillet with the sautéed vegetables. Stir well to combine all ingredients evenly. Bring to a gentle simmer over medium-low heat for about 5 minutes, stirring occasionally, to allow the flavors to meld together. I always taste at this point to make sure the sweet, savory, and tangy balance feels right before baking.
Preheat your oven to 325°F. Pour the entire mixture from the skillet into a 9x13 inch baking dish (or similar size casserole). Distribute the reserved bacon pieces evenly over the top of the bean mixture. The bacon will finish crisping during baking and infuse additional smoky flavor into the beans.
Bake uncovered at 325°F for 2 hours. The low temperature allows the beans to absorb all the flavors gently while the top develops a slightly caramelized appearance. Stir the mixture halfway through baking to ensure even cooking and prevent the bottom from sticking.
Remove the baking dish from the oven and let it stand for 5-10 minutes before serving. This resting period allows the flavors to settle and the mixture to thicken slightly as it cools a bit, making it easier to serve and more cohesive on the plate.