Preheat oven to 350 degrees. Grease 9x13-inch casserole dish. Mix the 2 cheeses together. Mix chicken, yogurt, peppers, garlic powder, salsa, onion, chili powder and chicken soup. Place 1/2 cup of chicken mixture on center of a tortilla shell. Sprinkle with 2 T cheese. Spread to within half an inch of the edge of the shell. Roll up and place seam side down in casserole dish. Repeat until all shells are filled. Cover with foil and bake for 30 minutes. Remove foil. Top with additional shredded cheese and bake another 15 minutes. Serve with sour cream, lettuce and tomato.