In a mixing bowl, combine the almond milk, chia seeds, mashed banana, cocoa powder, maple syrup, vanilla extract, and salt. Whisk until well combined and there are no lumps.
Let the mixture sit for about 5 minutes, then whisk again to prevent the chia seeds from clumping together.
Cover the bowl and refrigerate for at least 2 hours or overnight to allow the chia seeds to absorb the liquid and thicken the pudding.
Once the pudding has set, stir it well before serving.
Divide the pudding into serving bowls and top with chopped hazelnuts. Enjoy chilled.