Mash the banana: In a medium saucepan or microwave-safe bowl, mash a ripe banana until mostly smooth. Leave a few small chunks for texture.
Add liquids and oats: Stir in 1/2 cup rolled oats, 1/2 cup milk, and 1/2 cup water.
Add a pinch of salt and 1/2–1 teaspoon cinnamon.
Cook the oats: Stovetop: Bring to a gentle simmer over medium heat, stirring often, 4–6 minutes until creamy.
Microwave: Cook 2–3 minutes in a large bowl, stirring halfway. Watch for boil-overs.
Remove from heat and cool briefly: Let the oatmeal sit 1–2 minutes so it thickens slightly and cools. This prevents protein powder from clumping.
Mix in protein and vanilla: Stir in 1 scoop vanilla protein powder and 1/2 teaspoon vanilla extract.
Add a splash of milk if it gets too thick.
Finish with creaminess: Fold in 2–3 tablespoons Greek yogurt if using. Taste and add maple syrup or honey if you want it sweeter.
Top and serve: Sprinkle chopped walnuts or pecans, chia or flax seeds, and a few mini chocolate chips if you like. Enjoy warm.