Preheat the oven to 400 degrees. Spray an 8x8-inch baking dish with cooking spray. Spread ¼ cup of the salsa on the bottom of the baking dish.
In a medium mixing bowl, combine the chicken with the sour cream and ¾ cup salsa; mix well. Place 4 tortillas on the bottom of the baking dish over the salsa. Top with half the chicken mixture, half the cheese, half the tomatoes, and half the cilantro. Repeat the layers.
Bake uncovered for 20-25 minutes or until the cheese is melted and bubbly. Top with any additional toppings, if desired, and serve with extra salsa on the side.