Combine chicken, 1 cup salsa, and sour cream in large bowl. Spread ½ cup salsa on bottom of a 9 inch deep-dish pie plate, Press 1 tortilla into pie plate; top with half the chicken mixture. Sprinkle with an even layer of cheese and half the spinach. Repeat, reserving about ¼ cup cheese. Top with final tortilla; spread with the remaining ½ cup salsa and sprinkle with reserved cheese.
Cover with foil; bake 30 minutes. Remove foil and bake 15 more minutes until cheese melts.
To serve, slice into wedges.