1. In the bowl of a food processor fitted with the metal blade, combine beans, onion, jalapeno, garlic, red-pepper flakes, salt, and pepper. Pulse until smooth and thick; add water 1 tablespoon at a time, if necessary, to reach spreadable consistency. Transfer to 1 medium bowl, and stir in cilantro.

2. In another bowl, gently toss avocado with lime juice to prevent browning.

3. Assemble the sandwiches: Spread black-bean mixture on two slices of bread; layer one slice with smoked turkey and tossed avocado, and place the other slice on top of it. Using a serrated knife, trim crusts and cut into triangles. Cover with a damp paper towel until ready to serve.