Preheat the broiler. Puree the black beans, chili powder, cumin, and cayenne in a blender or food processor, adding a tablespoon of oil (or water) at a time to help the mixture move. I pureed for a minute or two but still left some texture.
In a food processor or blender, puree the cilantro, yogurt, garlic, and salt, adjusting the seasoning with more cilantro/salt/yogurt to your tastes.
Place tortillas in the oven directly on the rack, taking care that the edges are supported (otherwise they will bend through the cracks and it will be bent in a funny shape). Let the tortillas bake for 3 5 minutes on both sides until they are browned and crispy.
Top the crispy tortillas with black beans, tomatoes, avocados, and lettuce. Drizzle with cilantro sauce.
Healthy Black Bean Tostadas with Cilantro Sauce · Dinner Match Lab | Dinner Match Lab