Preheat the oven to 350 °F (175 °C) and grease a 9" pie pan.
In a large mixing bowl, stir together the filling ingredients. Spread the apples evenly over the bottom of the prepared pie pan.
4 cups firm baking apples, 2 teaspoons ground cinnamon, 3/4 teaspoon ground cardamom, 1 tablespoon raw sugar
In another large mixing bowl, stir together the the topping ingredients, just until combined. Spread the topping over the apples.
9 tablespoons (126 grams) refined coconut oil, 1/2 cup (100 grams) raw sugar, 1/4 cup (80 grams) maple syrup, 1 1/2 tablespoons vanilla extract, 1 1/4 cups (113 grams) rolled oats, 3/4 cup + 1.5 tablespoons (78 grams) oat flour, 1/2 teaspoon baking powder, 1/4 teaspoon salt
Bake for 40-45 minutes or until the apples are bubbly and the topping is firm.
Serve warm, room temperature or cold. I recommend letting it sit for about 3-4 hours or until it's cooled. This allows the flavors to come together better and it's much easier to cut. When still warm, it's more like a crumble and you won't get clean slices.
Cover and store at room temperature for up to 2 days. Refrigerate after that. This is great made a day or 2 ahead of time!