Add the old-fashioned oats to a large mixing bowl or a pint-sized mason jar.
Pour in the milk and stir well.
Add the strawberry Greek yogurt and mix until combined.
Stir in the chia seeds.
Fold in the diced strawberries.
If using, add the vanilla protein powder and mix thoroughly to prevent clumps.
If the mixture seems too thick, add ¼ to ½ cup water and stir.
Cover the container and refrigerate.
Let the Strawberries and Cream Overnight Oats chill overnight, or for at least 2 hours.
Stir before serving and add extra strawberries if desired.