Preheat the oven to 350˚F. Lightly spray a 9x9 inch square pan with cooking spray and set aside.
In a large bowl, mix together the filling ingredients. Pour into the prepared pan.
In a medium bowl, mix together all of the topping ingredients until fully combined.
Spread the topping ingredients evenly over the nectarine mixture, then bake in the preheated oven for 40-45 minutes, or until the top is golden brown and filling is bubbly. Allow to cool for at least 20 minutes before serving.