Mash the banana: In a jar or bowl, mash the banana with a fork until mostly smooth.
A few small chunks are fine.
Add the wet ingredients: Stir in the milk, Greek yogurt, honey or maple syrup, vanilla, and a pinch of salt. Mix until well combined.
Add the dry ingredients: Stir in the oats and cinnamon. If using chia seeds for extra thickness, add 1–2 teaspoons now.
Adjust sweetness and spice: Taste the mixture.
Add a little more honey or cinnamon if you like it sweeter or spicier.
Chill: Cover and refrigerate for at least 4 hours, ideally overnight. The oats will soften and thicken as they absorb the liquid.
Stir and serve: In the morning, give it a good stir. If it’s too thick, add a splash of milk.
Top with banana slices, nuts, or a drizzle of nut butter.
Take it to go: If you’re heading out, pack it in a lidded jar. Add toppings just before eating to keep them crisp.