Preheat your oven to 350°F (175°C) and lightly grease a small oven-safe baking dish or ramekin.
Place the rolled oats into a blender and pulse until they reach a fine, flour-like consistency.
In a medium mixing bowl, whisk together the oat flour, vanilla protein powder, ground cinnamon, ground ginger, and baking powder.
Add the egg whites, 0.25 cup of the Greek yogurt, and vanilla extract to the dry ingredients, stirring until just combined.
Fold in the grated carrots until evenly distributed throughout the batter.
Pour the mixture into the prepared baking dish and bake for 20 to 25 minutes, or until a toothpick inserted into the center comes out clean.
While the cake is baking, prepare the frosting by whisking the remaining 0.5 cup of Greek yogurt with the light cream cheese and maple syrup until smooth.
Remove the cake from the oven and let it cool for 5 minutes before spreading the cream cheese frosting over the top.
Garnish with chopped walnuts and enjoy warm.