Preheat your oven to 325°F and adjust the rack to a lower-middle position.

In a large sauté pan, cook the bacon until it's partially done and has released around 1/4 cup of fat. Set the bacon aside on paper towels to drain.

Using the bacon drippings, sauté the diced onion and green bell pepper in the same pan for about 5 minutes until softened.

Add the beans, along with the barbecue sauce, mustard, brown sugar, and vinegar to the pan. Bring the mixture to a gentle simmer. If your pan isn’t large enough, transfer the beans to a bigger bowl and stir in the remaining ingredients.

Transfer the simmering beans to a greased 13x9-inch oven-safe dish. Arrange the partially cooked bacon strips on top.

Place the dish in the oven and bake for approximately 2 hours, or until the beans are bubbly and the sauce thickens to a syrup-like consistency.

Once baked, let the beans sit for a few minutes to thicken further before serving.