In a large bowl, mash the bananas until smooth.
Add oats, cinnamon, baking powder, chopped walnuts, honey, milk, and grated carrot. Mix until everything is evenly combined.
Let the mixture sit for 5–10 minutes.
Lightly grease a baking dish or line it with parchment.
Pour the mixture into the dish and spread evenly. Tap lightly to remove air pockets.
Bake at 350°F (175°C) for 25–30 minutes.
Let the bake cool slightly.
In a bowl, mix yogurt, cream cheese, and honey until smooth and creamy.
Spread or spoon the frosting over the cooled bake. Top with chopped walnuts.
Slice and serve slightly warm or chilled.