1Spray 6-quart slow cooker with cooking spray. In small bowl, mix brown sugar and melted butter; spread evenly in bottom of slow cooker. Arrange pineapple slices on brown sugar mixture, cutting as needed to fit in one layer. Place cherry in center of each slice and around slices, as needed.
2Add enough water to reserved pineapple juice to measure 1 cup. Make cake batter as directed on box, substituting pineapple juice mixture for the water. Pour batter over pineapple and cherries.
3Cook on High heat setting 2 1/2 to 3 hours or until toothpick inserted in center comes out clean. Turn off slow cooker; uncover. Remove ceramic base from cooker to cooling rack. Cool 15 minutes.
4Place heatproof serving plate upside down onto ceramic base; carefully turn plate and ceramic base over. Remove ceramic base.