Mash the banana: In a bowl or jar, mash a ripe banana until mostly smooth. A few small chunks are fine.
Whisk the base: Add cocoa powder, vanilla, a pinch of salt, and sweetener if using.
Whisk with the banana to create a chocolatey paste.
Add liquid: Pour in milk and whisk until the cocoa fully dissolves and the mixture looks uniform.
Stir in dry ingredients: Add oats and chia seeds. Stir well so the chia doesn’t clump and every oat gets coated.
Adjust thickness: If you like it thicker, add a spoonful of Greek yogurt now. If you prefer it looser, add a splash more milk.
Chill: Cover and refrigerate for at least 4 hours, ideally overnight, to let the oats soften and the chia thicken the mixture.
Serve: In the morning, give it a quick stir.
Add a little milk if it’s too thick. Top with banana slices, nuts, or a drizzle of peanut butter.