Toast the walnuts (optional but recommended): heat a small dry skillet over medium heat and add the chopped walnuts and 1 tsp butter or a drizzle of neutral oil. Toast, stirring frequently, for 2–3 minutes until fragrant and edges are slightly darker. Remove from heat and cool. Why: toasting unlocks walnut oils and concentrates their flavor and crunch — it makes a simple breakfast feel elevated.

Mash one banana for creaminess: in a medium bowl, use a fork to mash one small banana until mostly smooth with a few small chunks remaining. Why: mashed banana acts as a natural sweetener and binder; it creates a custardy, creamy texture without dairy or eggs.

Combine dry ingredients: add 1 cup rolled oats, 1 tsp ground cinnamon and a pinch of fine sea salt to the bowl with the mashed banana. Stir to coat the oats in banana and cinnamon. Why: mixing the dry oats with the banana first helps distribute flavor evenly and prevents clumping when liquid is added.

Add liquids and flavor: pour 2 cups unsweetened almond milk and 1/2 tsp vanilla extract (if using) over the oat mixture. Add 2 tsp maple syrup or honey now if you prefer a sweeter result. Stir thoroughly until evenly combined. Why: the 1:2 oats-to-liquid ratio hydrates the oats fully and produces a creamy, spoonable texture after chilling; stirring ensures every oat flake absorbs liquid and flavor.

Mix in most walnuts and reserve some for topping: fold in about 1 tbsp of the toasted walnuts into the oat mixture, reserving the remainder for garnish. Why: folding some walnuts in gives intermittent crunch; reserving some for topping keeps the contrast of toasted texture and visual appeal.

Portion and chill: divide the mixture between two jars or airtight containers, smoothing the tops. Seal and refrigerate for at least 6 hours, preferably overnight. Why: chilling allows oats to fully hydrate and flavors to meld — the cold time is what transforms the raw oats into a creamy, ready-to-eat breakfast.

Finish before serving: when ready to eat, give each jar a vigorous stir to reincorporate any separated liquid and redistribute the banana. If the oats are thicker than you prefer, stir in up to 2–4 tbsp extra almond milk to loosen. Why: stirring restores a uniform texture and lets you adjust creaminess.

Top and present: top each serving with the remaining sliced banana and the reserved toasted walnuts. Drizzle a tiny extra 1/2 tsp maple syrup or honey over each if you want an extra shine and sweetness. Why: fresh banana adds brightness and walnut topping preserves crunch and adds a toasty aroma.

Optional warming (for a warm variation): microwave a jar for 30–45 seconds and stir; or warm in a small saucepan over low heat, stirring, until just heated through. Why: Overnight oats are traditionally eaten cold, but a gentle warm-up changes the texture to warm porridge while keeping the overnight creaminess.