In a medium bowl, combine rolled oats, chia seeds, oat milk, and a splash of vanilla extract. Mix until well incorporated.

Cover the bowl and refrigerate overnight, or for at least 2-3 hours to let the oats absorb the liquid.

In a mason jar, add a generous dollop of Nutella at the bottom before adding the oat mixture, leaving space for toppings.

Before serving, stir the mixture well, adding extra oat milk if necessary. Top with sliced bananas, chopped hazelnuts, and more Nutella.