Preheat the oven to 350°F (175°C).

In a skillet over medium heat, cook the diced bacon or sausage until browned and crispy.

Add the chopped onions to the skillet and cook until soft and translucent, about 5 minutes.

In a large mixing bowl, combine the navy beans, cooked bacon or sausage, sautéed onions, brown sugar, ketchup, apple cider vinegar, Worcestershire sauce, and mustard. Stir well to combine.

Season the mixture with salt and pepper to taste.

Pour the bean mixture into a 9x13 inch baking dish and spread it evenly.

Cover the dish with aluminum foil and bake for 1 hour.

Remove the foil and bake for an additional 30 minutes.

Let the beans sit for about 10 minutes before serving.