Preheat the oven to 350°F. I usually wait to turn the oven on until the bacon is almost done — that way it's preheated right when we need it.
Cook the bacon. Chop your bacon into bite-sized pieces and cook it right in a 10-inch cast iron skillet over medium heat until it's good and crispy. Pull it out onto a paper towel-lined plate to drain — but leave that bacon grease in the pan. That's where so much of the flavor comes from.
Sauté the veggies. While the bacon cooks, dice your onion and bell pepper. I love using my chopper for this — it makes very quick work of it. Add the veggies straight into the bacon grease over medium-low heat and cook for about 2 to 3 minutes until they soften up.
Drain and add the beans. While the veggies cook, open your three cans of pork and beans. Drain off most of the liquid from the top — you don't want too much liquid because we're adding a flavorful sauce. Pour the beans right into the skillet with the veggies.
Stir in half the bacon. Take about half of your cooked bacon and stir it into the beans. We'll save the rest to sprinkle on top before baking.
Add the sauce ingredients. Add the barbecue sauce, apple cider vinegar, maple syrup, and ground mustard right into the skillet. Give it a good stir until everything is mixed evenly. Let it bubble for a minute or two so the flavors come together.
Top with the rest of the bacon. Sprinkle the reserved bacon right over the top.
Bake at 350°F for 45 minutes. The beans will still look juicy when you pull them out — don't worry, that sauce thickens up as it cools. Give it a few minutes to rest before serving.