Just slice up your apple, layer it in a bowl with Splenda (or sugar) and either apple pie spice or pumpkin pie spice. I like pumpkin pie spice, it has ginger in addition to the apple pie spice ingredients.
Cover it with plastic wrap and microwave. For a Granny Smith apple, I microwave for 2 minutes. For other apple varieties, usually only 1 to 1 1/2 minutes. Stir and let cool just a bit before eating. I cooked a McIntosh apple for 2 minutes one time and ended up with warm applesauce.