Preheat oven to 375°F (190°C) and lightly grease an 8x8 inch square baking dish.
In a large mixing bowl, combine the rolled oats, ground flaxseed meal, baking powder, sea salt, and ground cinnamon.
In a separate bowl, whisk together the almond milk, maple syrup, melted coconut oil, and vanilla extract until emulsified.
Pour the liquid ingredients into the dry oat mixture and stir until fully incorporated.
Fold in your chosen mix-ins and transfer the batter into the prepared baking dish, spreading it evenly.
Bake for 30 to 35 minutes or until the edges are golden brown and the center is firm to the touch.
Remove from the oven and allow to cool for at least 5 minutes to set the structure before slicing and serving.