Preheat the oven to 350 degrees F. Spray a round cake pan with nonstick spray (butter flavored, if available) and set it aside.
To make the glaze: Put butter in a small microwave-safe bowl and microwave for about 15 seconds, just until melted. Add brown sugar and mix well. Set aside.
To make the cake: Combine cake mix with baking powder in a large bowl. Mix well with a hand mixer. Add club soda and applesauce, and stir until smooth. Set aside.
Spread glaze evenly along the bottom of the cake pan. Blot pineapple rings and cherries with paper towels to remove any excess moisture. Lay the pineapple rings in an even layer in the cake pan, and place one cherry in the center of each pineapple ring.
Evenly pour the batter into the cake pan over the fruit layer. Bake in the oven until a toothpick inserted into the center comes out clean, 30 to 35 minutes.
Allow the cake to cool for 15 to 20 minutes, until just slightly warm. Firmly and securely place a large plate over the pan, and carefully flip so the plate is on the bottom. Gently lift the pan to release the cake. If you have trouble releasing it, pop it in the oven for a few minutes.
Cut into 8 slices and dig in!
PER SERVING (1 slice, 1/8th of cake): 189 calories, 3.5g fat, 298mg sodium, 39g carbs, 0.5g fiber, 26.5g sugars, 1.5g protein