Place the diced apples in a small, microwave-safe dish and top with butter pieces. Microwave for 1 minute to soften the apples.
Add in the brown sugar, cornstarch, cinnamon and nutmeg and stir to coat the apples.
Add all topping ingredients to a separate bowl and use a fork to mash together until well combined. Sprinkle on top of the apple mixture.
Microwave for another 2 minutes, until golden brown and bubbly. Serve warm with vanilla ice cream and (optional) caramel sauce.
