Preheat your oven to 400 degrees, grease an 8x8 pan and set it aside.
Take a small bowl or cup and make your flax egg. Combining 2 TB flax meal with 4 TB water, stir, and let sit.
Take a medium mixing bowl and combine your dry ingredients; oats, brown sugar, white sugar, baking powder, cinnamon, and salt, and stir until well combined. Now add your wet ingredients; oat milk, flax egg, vanilla, and melted vegan butter, and stir until well combined.
Get your chopped apples and line them on the bottom of the 8x8 pan evenly as you can, then pour the oat mixture over the top of the apples.
Bake in the preheated oven for 30-40 minutes, checking at the 30-minute mark; it shouldn't be jiggly.