In a mason jar or lidded container, combine the rolled oats, protein powder, almond milk, vanilla, chia seeds, and maple syrup. Stir thoroughly until everything is well mixed.
Add the pistachio butter and stir lightly to create swirls of nutty flavor.
Seal the container and place it in the refrigerator for at least 4 hours, or ideally overnight.
When ready to eat, remove the container from the fridge and give it a quick stir. The protein powder, oats, and chia seeds will have absorbed most of the liquid, so you can add a splash of milk to reach your desired consistency.
Top with chopped pistachios, a drizzle of pistachio butter, or any additional toppings you love (e.g., berries or coconut flakes).
Serve and enjoy your deliciously creamy, nutrient-packed oats!