Preheat the oven to 350F

Combine rice and water in a microwave-safe bowl

Cover the bowl

Microwave rice mixture for 8 minutes

Fill a medium pot with water 3/4 of the way full

Add chicken to the pot

Bring to a boil over medium-high heat

Once boiling, reduce heat to low

Cover

Cook chicken for 15 minutes

Remove chicken from water and cut into 1-inch cubes

Coarsely chop the onion

Melt 1 tablespoon butter in a large skillet

Add onions

Cook, stirring frequently for 5 minutes

Drain the water chestnuts

Combine chicken, almonds, onion, rice, mayonnaise, cream soup, and water chestnuts in a large mixing bowl

Stir until completely mixed

Spray the 9x13 baking dish with cooking spray

Add ingredients to the baking dish

Melt remaining butter in the large skillet

Add frosted flakes to the butter

Stir until frosted flakes are coated in butter

Sprinkle the frosted flakes over the top of the mixture in the baking dish

Cover with foil

Bake in the preheated oven for 45 minutes

Remove the foil

Bake for an additional 15 minutes

Serve