Heat oven to 350°. Spray an 8×8-inch baking dish with nonstick spray.

In a large bowl combine oats, walnuts, cranberries, baking powder, cinnamon, allspice, salt and 2 tablespoons of the sugar until blended. Remove ½ cup of the mixture and set it aside in a small bowl.

In a blender or food processor puree the sweetpotato, bananas, eggs, vanilla, 1 cup of the milk, 2 tablespoons of the canola oil and remaining 2 tablespoons of the sugar until smooth. Add to the larger bowl of the oat mixture. Stir in remaining milk. Pour into prepared pan. Add remaining tablespoon of oil to the remaining oat mixture (in the smaller bowl). Stir; set aside.

Bake 10 minutes. Remove from oven. Sprinkle with oat mixture. Return to oven. Bake an additional 25 to 30 minutes, until puffed and golden brown.

Serve warm or at room temperature, topped with a dollop of yogurt or a drizzle of maple syrup, if desired.