Preheat the oven to 350° F (176°C) Add 1 cup of oats to a blender and blend for 30 seconds until it turns to oat flour. (You can also use 1 cup of oat flour instead of whole oats.)
Add the cup of blended oat flour to a mixing bowl with a cup of whole oats, 1/3 cup brown sugar, 2 tablespoons ground flax seeds, 2 teaspoons cinnamon, 1/2 teaspoon nutmeg, and 1/2 teaspoon salt then mix well.
Peel, core, and dice 2 cups of apples into bite-sized pieces. Then add the apples to the oatmeal mixture and stir well.
Add 2 cups of plant-based milk of choice and mix well. Pour the mixture into a greased baking dish, then set aside while you prepare the crumble topping. (This allows the milk to soak into the oatmeal and soften it a little before baking.)
Make the crumble topping (optional)
In a small bowl, mix vegan butter, flour, whole oats, brown sugar, cinnamon, baking soda, and salt together until it becomes well incorporated and crumbly. Sprinkle the crumble on top of the oatmeal mixture. (optional)
Bake at 350° F (176°C) for 35 minutes until dry and slightly browned on the top. Allow cooling for 15 minutes before serving.
Notes
You can adjust the amount of sweetener used to suit your taste. I find that 1/3 cup makes it mildly sweet which works well when drizzling with extra syrup.
You can also make this dish without apples or other fruit. If you are going to omit the fruit, add an extra 1/4 cup of vegan milk to account for the moisture you are missing from the fruit.