Heat oven to 350°F. Spray 2-quart casserole with cooking spray. In medium bowl, mix 1 1/2 cups salsa and the sour cream.
Break taco shells into bite-size pieces. Place half of taco shell pieces in casserole. Top with shredded chicken and half of the salsa mixture. Top with half of the cheese. Repeat with remaining taco shell pieces, salsa mixture and cheese.
Bake uncovered about 30 minutes or until cheese is melted and top is golden brown. Let stand 5 minutes before serving. Serve with additional salsa.