• Make the flax egg: Stir one tablespoon of ground flaxseeds with three tablespoons of lukewarm water. Set it aside for 10 minutes and use it as a flax egg in the recipe.
• Preheat the oven to 350°F (180°C). Spray oil in an 8-inch x 8-inch square baking dish. Set aside.
• In a large bowl, whisk the flax egg, milk, yogurt, peanut butter, vanilla, and maple syrup.
• Whisk in the vanilla protein powder until no lumps show.
• Stir in the remaining dry ingredients: rolled oats, chia seeds, salt, and cinnamon.
• Fold in the mixed berries and stir to combine.
• Pour the mixture into the prepared baking dish.
• Bake on the center rack of the oven for 40 minutes for a soft creamy texture or up to 50 minutes for a firmer texture.
• Keep it in the oven until the baked oatmeal is set, not jiggly in the center, and golden brown on top. It will firm up as it cools in the pan at room temperature.

Storage

• Cool down completely and store in the fridge, in its baking dish covered with a piece of foil for up to 4 days.

Serving

• Serve cold or lukewarm with a dollop of non dairy Greek yogurt or extra almond milk.