01 - Preheat oven to 350°F. Grease an 8x8-inch baking dish with butter or cooking spray.
02 - In a large bowl, whisk together eggs, milk, melted butter, maple syrup, and vanilla extract until smooth and well combined.
03 - Add oats, baking powder, cinnamon, nutmeg, and salt to the wet mixture. Stir until all ingredients are evenly distributed and oats are fully coated.
04 - In a separate bowl, toss diced apples with lemon juice, brown sugar, and cinnamon until apples are evenly coated.
05 - Gently fold the seasoned apple mixture into the oat batter, taking care not to overmix.
06 - Pour the oatmeal mixture into the prepared baking dish. Use a spatula to spread the batter evenly, ensuring apples are distributed throughout.
07 - Bake for 35-40 minutes, or until the top is golden brown and the center is just set (a toothpick inserted should come out mostly clean).
08 - Let the baked oatmeal cool for 5-10 minutes before cutting. This allows it to set and makes serving easier.
09 - While oatmeal cools, mix Greek yogurt with 2 tbsp maple syrup in a small bowl until smooth and creamy.
10 - Cut baked oatmeal into squares. Serve warm or at room temperature topped with a generous dollop of sweetened yogurt and a sprinkle of toasted nuts, if desired.