Preheat your oven to 350°F (175°C). Lightly grease an 8x8 inch baking dish with coconut oil or cooking spray. This ensures your crisp won't stick and makes cleanup a breeze.

Prepare the topping by combining the oat flour, rolled oats, coconut sugar, chopped pecans, 1/2 teaspoon cinnamon, and salt in a large mixing bowl. Stir until all dry ingredients are well distributed.

Add the cold, cubed vegan butter to the dry topping mixture. Use your fingertips to work the butter into the dry ingredients, squeezing and rubbing until a coarse, crumbly mixture forms, resembling wet sand. Alternatively, use a pastry cutter. Chill the topping in the refrigerator while you prepare the apples; this helps maintain its crisp texture during baking.

In another large bowl, combine the thinly sliced apples, maple syrup, 1 teaspoon cinnamon, nutmeg, and vanilla extract. The thin slices allow for even cooking. Toss gently until the apples are thoroughly coated.

Crucially, sprinkle the cornstarch or arrowroot powder over the apple mixture and toss again until well combined. This step is vital for preventing a watery or soggy bottom, ensuring your apple filling thickens beautifully as it bakes.

Pour the apple mixture evenly into the prepared baking dish. Distribute the chilled crumb topping evenly over the apples, making sure to cover the entire surface.

Place the baking dish on a baking sheet to catch any potential overflow from bubbling juices during baking. Bake for 45-55 minutes, or until the topping is golden brown and the apple filling is visibly bubbling around the edges. Bubbling indicates the cornstarch has activated.

Remove the healthy apple crisp from the oven and let it cool on a wire rack for at least 10-15 minutes before serving. This cooling time allows the filling to set further. Serve warm with a scoop of your favorite dairy-free vanilla ice cream or a dollop of coconut whip for a truly exquisite dessert.