Combine cinnamon, ginger, nutmeg and maple syrup in small pan. Using a whisk, stir constantly over low temperature, just until mixture starts to simmer. Set aside to cool.
In medium skillet, melt 4 Tblsp. butter and add cubed Spam. Cook over medium heat until cubes are light, golden brown, stirring them around with wooden spoon or spatula. Remove from skillet & drain on a paper towel to eliminate any excess grease.
Use remaining 1 Tblsp. butter to coat inside of 2.5 quart caserole.
In prepared casserole, layer half the apples, half the onion slices, half the cubed Spam, then pour half the syrup mixture over. Repeat layers, ending with remaining syrup mixture.
Cover casserole with lid or with aluminum foil (seal tight) and bake @ 375°F until apples and onions are tender, about 20-25 minutes.
Open biscuits and separate; arrange over casserole, leaving a little space between each one.
Bake, uncovered, @ 375°F for another 10-12 minutes, until biscuits are baked and light brown.