01 - Preheat oven to 350°F. Lightly 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 fully incorporated.
03 - Add oats, baking powder, cinnamon, nutmeg, and salt to the wet mixture. Stir until evenly combined.
04 - In a separate bowl, toss diced apples with lemon juice, brown sugar, and cinnamon until coated.
05 - Fold the apple mixture into the oat mixture. Pour into the prepared baking dish and spread into an even layer.
06 - Bake for 35–40 minutes until the top is golden brown and the center is set.
07 - Let the baked oatmeal cool for 5–10 minutes before cutting.
08 - While the oatmeal cools, mix Greek yogurt with 2 tablespoons maple syrup until smooth and creamy.
09 - Cut into squares and serve warm or at room temperature with a dollop of sweetened Greek yogurt and chopped nuts, if desired.