1Prepare a 5-6 quart slow cooker with nonstick spray or grease well with margarine.
In small bowl, mix apple mixture ingredients: set aside
2To make crumble mixture, in medium bowl, stir together oats,1/2 cup of brown sugar or Splenda brown sugar and the light salt. With a pastry blender or fork, cut in 1/2 cup of butter or light margarine until well combined. Set aside.
3In large bowl, mix cake batter ingredients until well combined.
In bottom of slow cooker, spread half of apple mixture. Top with half of crumble mixture and with half cake batter. Repeat layering again with remaining apple mixture, crumble mixture and cake batter
4Cover: cook on high heat setting 3 hours to 3 hours 30 minutes or until cake is set in center
Turn off slow cooker. Remove cover; let stand 15-20 minutes.
When reading to serve, invert coffee cake onto serving plate.
Serve: With light Cool whip or vanilla sugar-free icecream