Preheat your oven to 350°F and lightly grease a small oven-safe loaf dish or ramekin with a tiny amount of ghee.
In a medium mixing bowl, mash exactly half of the banana until smooth, then whisk in the egg whites, Greek yogurt, and vanilla extract until well combined.
Fold in the oat flour, cinnamon, baking powder, and sea salt, stirring until the batter is uniform.
Pour the mixture into the prepared dish and bake for 25 to 30 minutes until the center is firm and the top has risen.
While the bread bakes, slice the remaining half of the banana into thin rounds.
Heat the ghee in a small non-stick skillet over medium heat and sauté the banana slices for 2 minutes per side until they are golden and caramelized.
Remove the bread from the oven, top with the warm caramelized bananas and crushed walnuts, and enjoy immediately.