In a mason jar or airtight container, whisk together the rolled oats, protein powder, ground cinnamon, and salt.

Add the milk, Greek yogurt, vanilla extract, and maple syrup to the dry mixture.

Stir vigorously until the protein powder is fully incorporated and no dry clumps remain.

Seal the container with a lid and refrigerate for a minimum of 6 hours, preferably overnight.

Before serving, stir the mixture and garnish with an additional sprinkle of cinnamon or a dollop of yogurt if desired.