Whisk the base. In a large bowl, whisk the Greek yogurt, milk, protein powder, honey, vanilla, and cinnamon until completely smooth (no protein-powder lumps — whisk well; they won’t dissolve overnight).
Fold in the oats and chia. Stir in the oats and chia seeds until every oat is coated.
Jar it up. Divide among 4 mason jars or containers, about 1 cup each. Top each with 1/2 cup berries.
Chill overnight. Refrigerate at least 8 hours (or up to 5 days — the oats soften more each day, and I actually like day 3 best).