Add the grated apples and water to a saucepan and cook over medium heat for about 5 minutes, stirring occasionally, until the apples soften.
Stir in the oat flakes and let them absorb the liquid for another 3–5 minutes, stirring occasionally.
Add the chopped walnuts, vanilla extract, and melted butter or coconut oil. Mix well.
If using, stir in dried cranberries or raisins for added sweetness.
Remove from heat and let sit for a minute before serving.
Serve warm, optionally topped with extra nuts, cinnamon, or a drizzle of honey.