Preheat the oven to 400˚F.
Crust: In a medium bowl, mix together all of the crust ingredients until fully combined.
Lightly spray a pie pan, and press the dough into the pan. Bake in the preheated oven for 15-20 minutes.
Filling: Meanwhile, steam the asparagus until desired tenderness. Set aside.
In a medium skillet, heat the butter on medium heat. Cook the onion until fragrant. Set aside.
In a medium bowl, beat together the eggs. Add in the mozzarella, feta and milk, and mix together.
Place the asparagus and onions on the bottom of the pie pan. Pour the egg mixture over the asparagus.
Turn the oven down to 375˚F, and bake for 35-45 minutes.