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 until smooth.
If the mixture appears too thick, stir in ¼ to ½ cup water until the desired consistency is reached.
Cover the container and refrigerate.
Allow the Strawberries and Cream Overnight Oats to chill overnight, or for at least 2 hours.
Stir before serving and add extra strawberries if desired.