Sprinkle 1/3 packet of sugar substitute and 1/3 teaspoon pumpkin pie spice in the bottom of a microwave-safe bowl. Layer 1/4 of the apple pieces into the bowl; repeat. Spread the pumpkin over the apples. Sprinkle the remaining sugar substitute and pumpkin pie spice on the pumpkin. Top with the remaining apples. Pour the water over the mixture.
Cook in microwave on high for 3 1/2 minutes, stirring every minute.