Spread caramel in the bottom of a greased 8 inch / 20 cm cake pan. Lay apples on top. Set aside.
In a bowl, whisk together gluten-free flour, salt, baking soda, baking powder, and cinnamon. In a separate bowl, mix together oil, brown sugar, granulated sugar, non-dairy milk, flax egg, vanilla extract, and apple cider vinegar.
Add the dry ingredients into the wet ingredients and mix until combined. Let the batter rest for about 20-30 minutes to let the gluten-free flour hydrate.
While the batter is resting, preheat the oven to 350°F / 180°C. Pour the batter over the sliced apples, even the top with a spatula, and bake it in the preheated oven for 40-45 minutes, or until a toothpick inserted into the center comes out clean. Let it rest for at least 10 minutes before turning it out onto a plate or platter.