Preheat oven to 350°F.
Place tortillas on a large baking sheet, and bake for 10 minutes, or until crispy. Let cool.
Meanwhile, mix together crabmeat, lime zest and juice, mayonnaise, paprika, garlic powder, chopped cilantro, chili flakes, and a pinch of salt in a large bowl until combined. Refrigerate until ready to build the tostada.
Place black beans, chili powder, 2 tablespoons water, and a pinch of salt in a blender. Blend until it reaches a smooth, saucelike consistency.
Mash avocado with cumin and 1/8 teaspoon salt in a medium bowl.
Adapted from True Roots: A Mindful Kitchen with More Than 100 Recipes Free of Gluten, Dairy, and Refined Sugar. Copyright © 2018 by Kristin Cavallari.