Preheat the oven to 400°F and grease or line a 12-count muffin tin with cupcake liners. If using a silicone muffin tin, grease with cooking spray.
In a large bowl, whisk together the gluten-free flour, almond flour, tapioca, baking powder, baking soda, granulated sugar, brown sugar and salt. Mix until well combined.
Use your rubber spatula or spoon to make a well in the center of the dry ingredients. Add oat milk, butter, oil, eggs, and vanilla extract. Mix until a batter forms.
Fold in the chopped apples until combined. Set the batter aside.
In a medium bowl, make the crumb topping by mixing together the light brown sugar, cinnamon, melted butter and gluten free flour. Mix until it resembles small pebbles. Set aside.
Scoop about ⅓ cup muffin batter into each muffin liner. You may have extra batter at the end to make an additional 2-3 muffins; cook later or add to a second pan if you have. Top each muffin with generous amount of the crumb topping.
Bake muffins for 5 minutes at 400°F, then lower the oven temperature to 350°F and bake for an additional 20-25 minutes or until a toothpick inserted into the center of the muffin comes out clean.
Allow muffins to cool before popping out of the pan and eating or storing.