To make the salsa: In a small bowl, combine the tomatoes, avocado, onion, pepper (if desired), salt, and lime juice.
To make the beans: In a blender or food processor, combine the beans, hot sauce, and water. Blend or process until smooth. Pour the bean mixture into a saucepan and heat over low heat. Arrange the tortillas on a baking sheet or place them directly on the oven rack and bake for 6 to 10 minutes, turning once, or until they become crispy and start to brown.
Top each tortilla with some of the warmed black beans, salsa, and lettuce before serving.