- Preheat oven to 375°F
- Mix flour, oats, sugar and ¼ t cinnamon in a medium mixing bowl. Use a pastry cutter to cut in butter until mixture looks like wet sand and there are no lumps larger than a pea. Stir in walnuts
- Place all remaining ingredients in a large bowl, toss to combine. Move apple mixture to an 8x8 baking dish. Top with oat mixture.
- Bake until golden, about 45 minutes.
Best served warm with vanilla ice cream