Preheat oven to 350 degrees F. Grease a 9×13″ pan with coconut oil or non-stick cooking spray. Set aside.
In a medium bowl, mix together oatmeal, flour, cinnamon, salt, and baking powder.
In a large bowl, mix together egg, coconut oil, brown sugar, and vanilla extract until combined. Add dry ingredients to wet ingredients and stir until formed into dough. It will look crumbly. Set aside.
In a medium bowl, mix together berries, corn starch, lemon juice, and honey until evenly coated. Stir berry mixture into the oatmeal mixture. Pour into greased pan and spread evenly. Again, it will look crumbly; just spread as evenly as possibly.
Bake for 25-35 minutes until edges are golden brown. Can eat warm with milk/ice cream or store in an air-tight container in refrigerator.
*Oat flour can be made by putting rolled oats in a blender and grinding it into a powder. Measure out 1 1/4 cups of oat flour after grinding.