Preheat the oven to 375°F and spray an 8x8 or 9x9-inch baking pan with nonstick spray.
Whisk the eggs together in a large bowl, then pour in the milk, applesauce, and maple syrup and whisk to combine.
3 large eggs, 1½ cups milk, 1 cup applesauce, ½ cup maple syrup
Add in the baking powder, cinnamon, apple pie spice, and salt and whisk again.
1 teaspoon baking powder, 1 teaspoon ground cinnamon, 1 teaspoon apple pie spice, ½ teaspoon kosher salt
Finally, mix in the oats and ¾ of the apples.
3 cups old-fashioned oats
Cover the bowl and let it sit for 10 minutes then pour it into the baking pan and sprinkle the remaining apple pieces on top.
2 apples
Bake for 30-40 minutes, or until the center is no longer jiggly.
Let it rest for 15 minutes before slicing and serving with maple syrup if desired.