Preheat oven to 350 degrees Fahrenheit.
In a medium mixing bowl, combine the flour, salt, and baking powder. Add butter and cut into flour with a pastry cutter or fork until butter is the size of small peas. Add enough cold water to the flour mixture to form a ball.
Lightly grease a 9 x 13" cake pan or pyrex casserole dish. Place the dough in the pan and use your hands to flatten the dough out to cover the bottom of the pan. Continue pressing dough to cover pan about 1/2 of the way up the sides.
Bake crust in 350 F oven for 20 minutes. While the crust is baking, prepare the filling.
Sautee asparagus and green onions in 1 tablespoon of vegetable oil or butter. When the vegetables are tender, remove from heat and set aside.
In a medium mixing bowl, lightly beat eggs. Add the milk, garlic salt, and pepper and combine well.
Remove crust from oven. It is ready when dough in the center is set, but not browned.
Spread sauteed vegetables over crust.
Pour egg mixture over vegetables.
Sprinkle shredded cheese over the egg mixture and bake quiche in 350 F oven for 40 minutes, or until knife inserted in the center comes out wet, but clean. Cool for 10 minutes and serve.