01 - Preheat oven to 350°F. Grease an 8x8-inch baking dish with cooking spray or butter.
02 - In a large bowl, whisk together the eggs, milk, melted butter, maple syrup, and vanilla extract until smooth and fully incorporated.
03 - Add oats, baking powder, cinnamon, nutmeg, and salt to the wet mixture. Stir until all ingredients are well combined and the oats are evenly coated.
04 - In a separate bowl, toss the diced apples with lemon juice, brown sugar, and cinnamon until the apples are evenly coated.
05 - Fold the apple mixture into the oat mixture, ensuring the apples are distributed throughout.
06 - Pour the mixture into the prepared baking dish and spread evenly with a spatula.
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 clean).
08 - Let the baked oatmeal cool for 5–10 minutes before serving.
09 - Meanwhile, 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 with a generous dollop of sweetened Greek yogurt and a sprinkle of toasted nuts, if desired.