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.
03 - Add oats, baking powder, cinnamon, nutmeg, and salt to the wet mixture. Stir until well combined.
04 - In a separate bowl, toss diced apples with lemon juice, brown sugar, and cinnamon until evenly coated.
05 - Gently fold the apple mixture into the oat mixture until distributed throughout.
06 - Pour the mixture into the prepared baking dish and spread into an even layer using a spatula.
07 - Bake for 35–40 minutes until the top is golden brown and the center is just set.
08 - Let the baked oatmeal cool for 5–10 minutes before cutting.
09 - While cooling, mix Greek yogurt with 2 tbsp maple syrup until smooth and creamy.
10 - Cut into squares and serve warm or at room temperature with a dollop of sweetened Greek yogurt and chopped nuts, if desired.