Grease a 1.5 quart baking dish or 9x9 baking dish with vegan butter or cooking spray. Preheat the oven to 375 degrees Fahrenheit.
Place sliced peaches and lemon juice in a medium bowl. Sprinkle the arrowroot starch, cinnamon, and salt over them. Stir until all peaches are coated then add maple syrup and vanilla extract to the peach filling and stir again. Set aside.
Place two cups of oats into the bowl of a food processor. Process on high until you have a fine flour consistency. Transfer the oat flour to a second medium mixing bowl.
Add the coconut sugar, cinnamon, and salt to the oat flour. Pour melted butter and almond extract into flour mixture and stir to combine. Fold in remaining ½ cup of oats.
Transfer the peach mixture into the prepared baking dish. Top with pieces of crumble dough. Scatter topping evenly over prepared fruit. I like to press some of the topping into little pieces. Bake for 30 to 40 minutes, or until fruit is bubbling and topping has started to brown.
The crumble is best served warm, but can be stored in an airtight container in the refrigerator for up to 3 days. Serve with vanilla ice cream or coconut whipped cream.
Oat flour - You can opt to use store-bought gluten-free oat flour instead of making your own with the oats. Substitute two cups of gluten-free oat flour for two of the cups of gluten-free oats called for in the recipe.
If there is a dietary restriction or allergy, be sure to purchase certified gluten-free oats.
Frozen peaches can be substituted. If using frozen, do not thaw beforehand.