Preheat the oven to 375 °

For the apple filling:
In a large heavy pot, combine ⅓ cup water, half the honey, apples, raisins, cornstarch, cinnamon, and nutmeg. Bring to a simmer over low heat and cook, stirring occasionally, until the apples are soft, about 25 minutes. Lightly spray an 8 × 8-inch or 9 × 9-inch ceramic baking dish with oil. Put the apples into the bottom of the prepared baking dish.

For the oatmeal:
In a bowl, combine the oats, baking powder, and a pinch of salt. Pour over the apples. In a separate bowl, whisk together the milk, egg, rest of the honey, and vanilla. Pour the milk mixture over the oats, making sure to distribute the mixture as evenly as possible. Bake until the top is golden brown and the oatmeal is set, about 30 minutes. Cut into rectangles and serve warm