Preheat the oven to 425°F (220°C). Spray a 9x13-inch baking dish with nonstick cooking spray.
In a mixing bowl, combine the shredded rotisserie chicken and the taco seasoning packet until the chicken is evenly coated; set aside.
Place the baby spinach, fresh cilantro, and salsa in a food processor or blender and pulse until finely chopped and combined into a thick mixture.
Layer six 6-inch tortillas in the bottom of the prepared baking dish, overlapping slightly to cover the surface.
On the first layer, sprinkle 1 cup of shredded Mexican blend cheese, then half of the drained black beans, half of the drained corn, and half of the seasoned chicken. Spoon about 1 cup of the spinach-cilantro-salsa mixture evenly over the chicken.
For the second layer, place remaining tortillas, then the remaining beans, corn, seasoned chicken, and spread the rest of the spinach mixture on top. Finish with the remaining cheese evenly sprinkled over the top.
Cover the dish with aluminum foil and bake for 30 minutes, until the cheese is bubbly.
Remove the foil and bake an additional 10–15 minutes, or until the top is browned to your liking.
Let the lasagna rest briefly, then slice and serve warm with optional toppings such as jalapeños, plain Greek yogurt or low-fat sour cream, and extra cilantro.
