In a medium bowl, toss the shredded chicken with the scallions, chili powder, and lime juice until well combined.
Distribute the tortillas on a clean countertop — I like to fill and assemble the flautas all at the same time for efficiency, but you can do them in batches. Spoon about 2 tablespoons of the refried beans on the bottom of the tortilla and spread it out over the bottom half, smearing it all the way to the bottom edge. Spoon 2 tablespoons of the chicken mixture over the bare top half of the tortilla, distributing it evenly. Sprinkle 2 tablespoons of shredded cheese over the chicken. Tightly roll the tortilla from the top down, sealing the flauta with the bean covered part of the tortilla. Place them on the prepared baking sheet seam side down.
Brush the top of the flautas with the olive oil. Bake for about 15 to 20 minutes until browned, hot, and crispy. Serve with the salsa, guacamole, and sour cream, and shredded lettuce if desired.
Notes
Baked flautas can be stored in a container in the fridge for up to 3 days. Reheat and re-crisp them in a 325 F oven on a baking sheet for about 8 minutes. You can also freeze flautas.
You can freeze them filled and unbaked, packing them carefully in a freezer-proof container without any excess air. You can bake them directly from frozen; brush them with the oil, and add an additional 7 to 10 minutes of baking time.
Or you can freeze them after they have been baked and cooled, packing them into a freezer-proof container or zipper-top bag and pressing out excess air. To reheat from frozen just heat them through in a 350 oven for about 12 minutes until warm throughout.