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 well combined and smooth.
03 - In a separate bowl, combine the rolled oats, baking powder, cinnamon, nutmeg, and salt. Stir to distribute spices evenly.
04 - Add the dry ingredients to the wet mixture. Stir gently until just combined, being careful not to overmix.
05 - Pour the batter into the prepared baking dish and spread evenly with a spatula.
06 - Bake for 30–35 minutes, or until the oatmeal is set and golden brown at the edges. A toothpick inserted in the center should come out clean.
07 - Allow the baked oatmeal to cool for 5–10 minutes before slicing into portions. Top each serving with Greek yogurt, banana slices, nuts if desired, and a drizzle of maple syrup or honey.