Heat oven to 350. Spray a 2-1/2-quart casserole dish w/ cooking spray. Spray a lg skillet w/ cooking spray. Place skillet over med-high heat.
Add ground turkey to skillet and cook until browned. remove from heat. Add onion, garlic powder, taco seasoning, and tomato sauce. Mix well.
In bowl, combine sour cream and cottage cheese. Place 1/2 the crushed tortilla chips in bottom of casserole dish. Add enough turkey mix to cover chips. Cover mix w/ 1/2 sour cream mix. Sprinkle w/ 1/2 cheese. Repeat layers. Bake, uncovered for 30 mins, or until cheese is melted.