Prepare the bananas: Peel and slice 2 bananas into coins. Mash the third banana with a fork until mostly smooth.
If you want to slow browning, toss the slices with a teaspoon of lemon juice.
Mix the base: In a bowl, whisk Greek yogurt, milk, maple syrup (start with 2 tablespoons), vanilla, and a pinch of salt until creamy. If you like a thicker, almost pudding-like set, whisk in chia seeds.
Add flavor: Stir the mashed banana and cinnamon (if using) into the yogurt mixture. Taste and adjust sweetness.
Remember the wafers or granola may add sweetness later.
Layer it up: In a glass dish or individual jars, add a thin layer of yogurt mixture. Top with banana slices, then a layer of wafers or granola if using. Repeat layers until you run out, finishing with yogurt on top.
Chill: Cover and refrigerate for at least 1 hour (4 hours is better) to let the flavors meld.
If you added chia seeds, chilling helps it thicken nicely.
Finish and serve: Right before serving, top with extra banana slices, a sprinkle of cinnamon, and a handful of coconut or nuts for crunch. Serve cold.