Preheat your oven to 350°F (175°C). Line a 15x10 inch sheet pan with foil and give it a light spray with nonstick cooking spray for easy cleanup.
In a large bowl, beat the softened butter with both the granulated and brown sugars until the mixture is light and creamy.
Fold in the Greek yogurt and mashed banana, mixing until everything is smoothly combined.
Gradually add the flour, salt, and baking powder to the wet ingredients, stirring gently until a soft, uniform dough forms.
Set aside about 1 cup of this delicious batter for the top layer.
Evenly spread the remaining dough onto your prepared pan using a spatula. This forms the base of your snack cake!
In a separate small bowl, gently mix the Nutella and softened cream cheese until it's a smooth, tempting swirl.
Spoon this creamy Nutella mixture over the dough on the pan, making sure to leave a nice 1-inch clear border around all the edges.
Carefully drop spoonfuls of the reserved cake batter over the Nutella layer. It doesn't have to be perfect – it'll bake beautifully!
Bake for approximately 24 minutes, or until the cake is golden brown and a toothpick inserted into the cake part (not the Nutella swirl) comes out clean.
Remove the pan from the oven and let the cake cool completely on the pan before you even think about cutting into it. This step is key for a perfect glaze!
While the cake cools, whisk together the powdered sugar and milk in a small bowl until you have a smooth, drizzly glaze.
Once the cake is completely cool, drizzle the sweet glaze generously over the top before slicing into squares and enjoying this wholesome treat!