I learned how to make this delightful "sandwich" from my dad's coworker's wife who is from Mexico. It's really very simple and basically a quesadilla, but somehow she made it seem more like a sandwich when she mentioned how she often packs these in her husband's lunch.
flour tortillas (white or whole wheat)
black beans (canned works)
grated or sliced Monterey Jack cheese
thinly sliced smoked turkey lunch meat
thinly sliced red onion
avocado, lightly mashed
Heat a skillet and add butter over medium heat. When butter is melted, swirl in pan and add one tortilla. Top tortilla with beans and lightly mash to help the beans stick to the tortilla. Layer cheese and then a layer of turkey on top (tear the slices to fit the tortilla so there's just one layer of turkey covering the tortilla). Add another tortilla on top.
Cook for a few minutes until the bottom tortilla is golden brown. Carefully flip the quesadilla to brown the other tortilla. You'll want the second tortilla to get covered in butter so it can get golden brown as well. My lazy way is to pick up the quesadilla with a spatula and before flipping it over, adding more butter, letting it melt, and swirling it around in the pan. This is always a little precarious as the ensemble could easily fall off the spatula at any moment...A better suggestion would be to butter the second tortilla before adding it to the pan--that way when it's flipped, the tortilla will already have the butter it needs. Cook the second tortilla side until it's golden brown.
Remove quesadilla from skillet. Remove the tortilla that's touching the turkey and layer red onion and tomato and avocado. Replace the tortilla. Cut into quarters. Eat warm. This "sandwich" is also good cold or reheated later. If eaten later, add red onion, tomato, and avocado just before eating to keep things fresh and unsoggy.