Preheat oven to 350°F.
Lightly grease an 8x8-inch glass or ceramic baking dish.
Place sliced apples in a large mixing bowl.
Drizzle lemon juice over the apples and toss to coat.
Add cinnamon, nutmeg, brown sugar, vanilla extract, and salt to the apples.
Stir well until apples are fully coated in the mixture.
Pour the apple mixture into the prepared baking dish and spread evenly.
In a separate bowl, combine oats, gluten free flour, brown sugar, salt, and cinnamon.
Add cold diced butter to the bowl.
Use your hands or a pastry cutter to mix until the topping is crumbly and butter is distributed.
Sprinkle the crisp topping evenly over the apple mixture.
Bake for 40 to 45 minutes, until the top is golden brown and edges are bubbling.
Remove from the oven and let cool for 10 to 15 minutes.
Serve warm with vanilla ice cream, whipped cream, or enjoy as is.