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, sauce like consistency.
Mash avocado with cumin and 1/8 teaspoon salt in a medium bowl.
Layer the tostada: tortilla, then crab mixture, top with black beans, then avocado.
500 Calorie Meal
One serving of tostadas and 1 cup of fresh strawberries (or any fruit from the 50-calorie list.)