Preheat oven to 350°. Chop nuts, set aside.
Melt butter in 12” oven-proof skillet. Remove from heat, stir in brown sugar and stir until well blended.
Drain pineapple reserving juice, set aside.
Arrange pineapple slices over sugar mixture. Place a cherry half in center of each slice. Sprinkle with nuts.
Add enough water to pineapple juice to make 1 1/3 cups liquid.
In bowl combine cake mix, liquid, eggs and oil; whisk until well blended and smooth.
Pour over pineapple in skillet. Bake 35-40 minutes.
Remove from oven Cool 5 minutes, loosen edges of cake and invert onto large serving plate. Cool slightly. Top with cool whip and serve.