In a bowl combine chicken, celery, rice, mayonnaise, mushrooms, lemon juice, salt, pepper, and cream of chicken soup. Mix ingredients until well combined.
Pour mixture into sprayed 9 x 13 inch dish and spread out evenly in the dish.
Combine corn flakes and butter until corn flakes are well coated with butter.
Spoon corn flake mixture evenly over chicken/rice mixture.
Place dish in a 400 degree oven for 15 minutes.
Remove dish from oven and sprinkle with sliced almonds.
Place dish back into oven for 5 more minutes. Serves 6-8.