I'm assuming you're talking about Pork and Beans without the pork? Many, many years ago in home ec class our teacher gave us this recipe and I've used it frequently:
one can beans
about 2 teaspoons mustard
a couple of tablespoons of brown sugar (depends on how sweet you like them)
about a fourth cup chopped onions
a good sized dash of worcestershire sauce
enough ketchup to make it red again (maybe a half cup or more)
a tablespoon or so of vinegar
bake at 350 degrees for about 45 minutes.
You can add bacon bits or top the casserole with slices of bacon if you wish. Add diced garlic if you like that flavor.