Preheat the oven to 350°F. Grease an 8×8 square baking dish and set aside.
In a medium bowl, mix together the oats, brown sugar, salt,baking powder, cinnamon, and almonds until fully combined.
In another medium bowl, whisk together the milk, egg, butter, and vanilla.
Arrange the chopped nectarines on the bottom of the prepared baking dish. Pour the oat mixture evenly over the nectarines. Pour the milk mixture over the oats. Shake the baking dish to make sure the milk covers the oats evenly. If you want, add a few sliced nectarines on top of the oatmeal.
Bake in the preheated oven for 40 minutes, or until the top is golden and oatmeal is set. Let the mixture cool for 5 minutes and serve warm.