In a large mixing bowl, combine the shredded chicken, cooked rice, black beans, corn, diced tomatoes with green chilies, salsa, cumin, chili powder, and garlic powder. Mix until well combined.
In a 9x13 inch baking dish, layer two of the flour tortillas to cover the bottom. You may need to cut the tortillas to fit.
Spread half of the chicken mixture evenly over the tortillas, then sprinkle half of the cheddar and Monterey Jack cheeses on top.
Repeat the layers by adding two more tortillas, followed by the remaining chicken mixture, and finally the remaining cheeses on top.
Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes.
After 25 minutes, remove the foil and bake for an additional 15 minutes or until the cheese is bubbly and slightly golden.
Remove from the oven and let it cool for about 5 minutes before slicing.
Garnish with freshly chopped cilantro and serve with a dollop of sour cream, if desired.