Preheat oven to 350 degrees Fahrenheit.
Lay apples in an oven-to-tableware or 9×13 baking dish lined with Gefen Parchment Paper.
Mix together remaining apple base ingredients and pour over apples.
Bake until the apples soften slightly.
Blend one cup of oats in a food processor until it becomes a coarse flour.
Add the additional ingredients for the crumble and pulse until the walnuts break up and the ingredients are well mixed.
Spread the crumble mixture over the softened apples and bake for 35 to 40 minutes or till slightly browned. Enjoy hot or cold.
To prepare in a slow cooker: Add apples to the crock and drizzle with water, lemon juice, cinnamon, and sweetener. Cover with the crumble ingredients. Cover and cook on low for eight hours.