Preheat the oven to 375°F.
In a small bowl, mix together the brown sugar, cinnamon, nutmeg, and oats. Add the softened butter and mix until well combined. Fold in the dried cranberries and chopped nuts.
Using a paring knife or an apple corer, remove the cores from the apples, being careful to leave the bottoms intact to hold the filling.
Place the apples in a baking dish. Fill each apple with the sugar-oat mixture, pressing down slightly to pack it in. Pour the warm water into the bottom of the dish around the apples. Bake in the preheated oven for 45-50 minutes, or until the apples are tender.
If using, drizzle caramel sauce over apples. Serve warm.