Add all ingredients except the walnuts to the prepared baking dish - bananas, pumpkin puree oats, brown sugar, baking powder, cinnamon, nutmeg, salt, milk, coconut milk, egg, melted butter, and vanilla extract.
2 1/4 cups old-fashioned rolled oats, 3 whole bananas, mashed, 1 cups milk of choice, 1 cup full-fat, canned coconut milk, 1/3 cup pumpkin puree, 1/4 cup brown sugar, 1 teaspoon baking powder, 2 teaspoons cinnamon, 1/2 teaspoon nutmeg, 1/2 teaspoon salt, 1 large egg, 1 teaspoon vanilla, 2 Tablespoons unsalted butter, melted