01 - Preheat the oven to 350°F. Grease an 8x8-inch baking dish with butter or cooking spray.
02 - In a large bowl, whisk together the mashed bananas, eggs, milk, maple syrup, vanilla extract, and melted butter until thoroughly combined and smooth.
03 - In a separate medium bowl, combine the rolled oats, baking powder, ground cinnamon, ground nutmeg, and salt. Whisk to distribute spices evenly.
04 - Add the dry ingredient mixture to the wet ingredients. Stir gently with a spatula or wooden spoon until just combined—do not overmix as this can affect texture.
05 - Pour the batter into the prepared baking dish. Use a spatula to spread the mixture evenly, ensuring uniform thickness for consistent baking.
06 - Bake for 30 to 35 minutes, or until the oatmeal is set in the center and golden brown around the edges. A toothpick inserted in the center should come out mostly clean.
07 - Remove from the oven and allow the baked oatmeal to cool for 5 to 10 minutes. This helps it set and makes slicing easier. Cut into 6 equal portions.
08 - Top each serving with a dollop of Greek yogurt, fresh banana slices, chopped walnuts or pecans if desired, and a drizzle of maple syrup or honey. Serve warm.