I found this leftover baked beans idea in the latest issue of Better Homes and Gardens.
Reheat and mash the leftover baked beans with lime juice and a hefty pinch of chili powder. Spread the mashed baked beans on crisp tostada shells, then top with shredded lettuce, onions, tomatoes, cilantro, and a sprinkle of cheddar cheese.
You can also substitute the leftover baked beans in this recipe with leftover refried beans or leftover cooked pinto beans.
Find more bean recipes here: The Complete List of Bean Recipes by BeansBeansBeans