Whisk chia seeds, vanilla almond milk, mashed banana, and 1 teaspoon maple syrup. Let the mixture sit, covered, in the fridge for at least 2 hours or overnight.
Before eating, stir well and top with 1 tablespoon chopped walnuts, the other 1/4 of the banana, sliced, and an additional 1/2 teaspoon of maple syrup.