Drain the black beans. Rinse them several times under running water. Put them into the bowl of a food processor or blender. Add the salsa, cilantro, and cumin. Process and let sit for at least 20 minutes for the flavors to mingle.
To assemble, put some of the bean dip on the tostada shell, then top with sour cream and salsa. Curl the lettuce leaf tightly, and cut in a Chiffonade over each tostada.
Notes
Even the whole recipe, which serves 4 is only 499 calories, so you can eat two! You can easily use a store-bought salsa, or make your own.
Top your tostada with steamed veggies, like broccoli, green beans, corn, carrots, what have you.
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