Preheat oven to 350°F. Spray an 11x7 or a 9x13 pan with nonstick cooking spray. Whisk eggs, mashed banana, brown sugar, and vanilla until smooth. Stir in 2 teaspoons cinnamon, salt, and baking powder. Stir in oats and milk. Spread in prepared pan. Stir 1 tablespoon granulated sugar and remaining 1/2 teaspoon cinnamon. Sprinkle over unbaked oatmeal. Bake for 28-34 minutes until oatmeal is browned and not jiggly in the center. Cool slightly before serving. Serve with syrup and/or fruit or vanilla yogurt. Store in refrigerator up to 2 days. You can also portion and freeze for quick morning breakfasts!