Preheat oven to 375 degrees F (190 degrees C). Spray an 8x8-inch glass baking dish with cooking spray.
Mix oats, brown sugar, oat bran, chia seeds, baking powder, cinnamon, orange peel, and salt together in a bowl. Whisk milk, eggs, honey, butter, and vanilla extract together in a separate bowl.
Layer strawberries into the prepared baking dish; top with oat mixture. Pour milk mixture over oat mixture and top with blueberries.
Bake in the preheated oven until lightly browned and set, 23 to 28 minutes.
