Microwave the stack of tortillas for 30 seconds, flipping halfway through. Tuck 1 tortilla into each cup of 2 standard 12-cup muffin pans, gently pleating the edges of the tortillas so that they fit snugly. Roll 24 small balls of aluminum foil and place them insides the cups; they'll help the tortillas hold their shape. Bake until the tortilla cups have hardened slightly on all sides, 10 to 12 minutes. Let cool slightly. (Leave the oven on.)
Meanwhile, combine the black beans, enchilada sauce, chicken and corn in a large mixing bowl. Toss until the ingredients are evenly combined.
Carefully spoon the filling into each cup until it is filled nearly to the brim. Sprinkle the cheeses on top of each tortilla cup. Bake until the cheese is melted and the filling is warmed through, about 15 minutes.
Sprinkle the top of each cup evenly with desired garnishes and serve warm.
Mash the avocados with the lime juice. Mix in the onion and season with salt and pepper. Flavor with one of the 3 following options.
For pomegranate guacamole, fold in the pomegranate seeds. Top with more seeds before serving.
For roasted jalapeno guacamole, fold in the diced roasted jalapenos.
For feta guacamole, fold in the feta cheese. Top with more feta before serving.