Preheat the oven to 375F and spray an 8-inch or 9-inch baking dish.
In a large bowl, combine the milk, eggs, honey, butter, and vanilla. Add the protein powder and mix. Add the oats and salt and combine the mixture into a thick batter. Combining the ingredients in this order ensures the even distribution and absorption of the protein powder.
Pour the oat batter into the prepared baking dish. Distribute the berries on top. Some will sink during baking, that's ok!
Bake:
Bake in the preheated oven for 35 minutes, a little longer if using a smaller (8-inch) pan. When the center is no longer wet, and the oat mixture has been set, remove it from the oven.
Serve:
Once the baked oatmeal has cooled down for 5 minutes, slice a square or spoon some of it into a plate. Serve topped with yogurt, additional berries, or a drizzle of nut butter.