Mash the banana: In a small pot or microwave-safe bowl, mash a ripe banana with a fork until mostly smooth.
Leave a few small chunks if you like texture.
Combine base ingredients: Add 1/2 cup rolled oats, a pinch of salt, 1 cup milk (or 3/4 cup milk + 1/4 cup water), and a sprinkle of cinnamon. Stir well.
Cook the oats: Stovetop: Bring to a gentle simmer over medium heat, stirring often, for 4–6 minutes until thick and creamy.
Microwave: Cook on high for 2–3 minutes, stir, then another 30–60 seconds until creamy. Watch for boil-overs.
Add protein powder: Remove from heat.
Stir in 1 scoop (about 25–30 g) protein powder. If the oats get too thick, add a splash of milk until smooth and silky.
Stir in peanut butter: Add 1–2 tablespoons peanut butter and mix until melted through. Taste and adjust with a touch of honey or maple syrup if needed.
Finish and top: Stir in 1/2 teaspoon vanilla extract if using.
Spoon into a bowl and top with banana slices, chopped peanuts, and an extra drizzle of peanut butter.