Toast the nuts. In a dry skillet over medium heat, toast walnuts or pecans for 2–3 minutes, stirring until fragrant.
Set aside. This quick step adds a big flavor boost.
Mash half the banana. In a small bowl, mash half the banana with a fork. Save the other half for topping.
The mashed banana naturally sweetens the oats.
Simmer the oats. In a small saucepan, combine oats, milk, mashed banana, cinnamon, and a pinch of salt. Bring to a gentle simmer over medium heat, then reduce to low. Cook 4–6 minutes, stirring occasionally, until thick and creamy.
Stir in protein powder. Remove the pan from heat.
Whisk in the protein powder and vanilla until smooth. If it gets too thick, add a splash more milk to loosen.
Finish with texture. Stir in half the toasted nuts. Spoon the oatmeal into a bowl and top with banana slices, remaining nuts, and seeds if using.
Drizzle with maple syrup or honey if you want extra sweetness.
Adjust and enjoy. Taste and adjust: more cinnamon, a pinch more salt, or a splash of milk for creaminess. Eat while warm and cozy.