Grease the inside of a standard sized loaf pan with butter or non-stick spray. Set aside.
In a small bowl, mash banana. Add yogurt, vanilla extract, and water; stir to combine.
In a large microwaveable dish, whisk together rolled oats, cinnamon, and protein powder. Add wet ingredients to bowl with dry ingredients. Use a spatula and stir until well combined.
Place dish into microwave and cook for 3 minutes. Remove dish from microwave, and use a spatula to transfer oatmeal into the loaf pan; spread evenly. Cover pan with plastic wrap and refrigerate for 10-20 minutes, or until oatmeal has set and is firm enough to slice. (I allowed mine to sit in the refrigerator over night. It popped right out of the pan and was very easy to cut into slices)
Melt butter in a frying pan over medium high heat.
Slice oatmeal loaf into 8 -12 even slices (each serving will be 2 slices). When butter has melted and is bubbling, lay slices of oatmeal in pan and allow them to cook for 2 minutes, or until lightly crispy. Flip slice and repeat on other side.