Heat oven to 350° and spray a 8×8 or 9×9 inch baking dish with cooking spray.
In a medium bowl, whisk the oats, flour, flax, baking powder, and salt until well combined.
In a large bowl, whisk the egg and then add the milk, maple syrup, coconut oil, and vanilla extract.
Fold the dry ingredients into the wet and mix just until well combined.
In a small bowl, gently stir the citrus juice with the strawberries and corn starch.
Pour ⅔ of the batter into the baking dish and smooth out evenly. Pour the berry mixture over it evenly, and then top with the chopped chocolate, also disbursing evenly. Pour the remaining batter over top and smooth over.
Bake for 22-24 minutes. It should have a light golden color when done. Let cool 15 minutes before cutting and serving.