Preheat the oven to 350°F.
Add the ground beef to a large oven-safe pot and cook until browned. Remove the beef and drain any excess grease.
Add the chopped bacon to the pot and cook until crisp. Remove the bacon, leaving the rendered bacon fat in the pot.
Add the diced onion and green bell pepper. Cook until softened and fragrant.
Return the ground beef to the pot. Add the baked beans, barbecue sauce, brown sugar, and mustard, then stir until combined.
Stir in the bacon, or reserve some or all of it for serving if you prefer a crispier texture.
Bring the beans to a simmer, cover the pot, and transfer it to the oven.
Bake for 1 hour.
Remove from the oven, allow the beans to cool slightly, and top with any reserved crispy bacon before serving.