Make the yogurt base: In a large bowl, combine 4 cups Greek yogurt (full-fat or 2%), 4 scoops vanilla protein powder, and 2 teaspoons vanilla extract. Whisk or stir for 1 to 2 minutes until smooth and thick. If the mixture is too dense to stir easily, add 2 to 4 tbsp of milk and mix until it loosens up slightly. Taste and add 1 tablespoons maple syrup (optional, to taste) if needed.
Divide and store: Spoon the yogurt base evenly into 4 containers. Keep 4 bananas whole and separate until ready to eat. Store 1 1/2 cups crushed graham crackers or vanilla wafers in a separate small container or zip bag so they stay crunchy.
Assemble when eating: Slice your banana right before serving. Layer into your container: yogurt base, banana slices, then 1. cups crushed graham crackers or vanilla wafers on top. Eat immediately so the crumbs stay crunchy.