Preheat the oven to 350°F (175°C) and lightly grease an 8x8 baking pan with coconut or avocado oil.
In a large mixing bowl, combine the oat milk, rolled oats, maple syrup, peanut butter, cocoa powder, vanilla extract, baking powder, ground flax seed, chia seeds, and salt. Mix well to combine.
Pour the oatmeal mixture into the prepared baking pan and spread it out evenly.
Bake in the preheated oven for 40 minutes, or until the oatmeal is set and a toothpick inserted into the center comes out clean.
Remove from the oven and let it cool completely in the pan.
In a small bowl, mix together the vanilla protein powder and non-dairy milk to make the frosting.
Once the oatmeal has cooled, drizzle the protein frosting over the top.
Slice the baked oatmeal into squares and enjoy! Store any leftovers in the refrigerator and reheat before serving, or enjoy cold.