Preheat the oven to 350 degrees F (175 degrees C). Grease an 8-inch pan with cooking spray.
Drain pineapple slices; set aside.
Stir together brown sugar and melted margarine in the prepared pan; spread evenly in the bottom of the pan. Place pineapple slices into brown sugar mixture. Place a cherry into the center of each pineapple slice and the center of the pan.
Beat together cake mix, cold water, and egg in a large bowl with an electric mixer on low speed for 30 seconds. Beat on medium speed for 3 to 4 more minutes. Pour batter evenly over pineapple and cherries in the pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 25 to 30 minutes. Cool in the pan for 5 minutes. Loosen edges and turn out onto a serving platter.
NOTE
Standard cake mixes come in 16.5 oz boxes - since recipe calls for 9 oz mix, and my box of mix was 16.5 oz, I made two cakes. One can of sliced pineapple has 10 slices, so worked just fine. Use ¼ cup brown sugar and 2 tbsp butter or margarine per 9 inch pan. I melted the butter in each pan, mixed in the brown sugar. Bake time was only an extra 3 minutes so that is probably due to oven variance. I did use the juice from the pineapple instead of water in the mix as it only made sense to do so. Came out perfect!
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