Wash asparagus and discard woody ends, then chop into bite-sized pieces.
Slice mushrooms, dice onion, and mince garlic.
Saute onion, mushrooms, asparagus, and garlic in olive oil over medium heat for about 6 minutes until mushrooms begin to soften and asparagus is bright green, stirring occasionally.
Meanwhile, press the pie crust into a pie plate and crimp the edges.
Arrange sauteed vegetables in the bottom of the pie crust, then top with shredded cheese. Thoroughly whisk together eggs, half & half or milk, mustard, and spices, then pour the egg mixture over the veggies.
Cover the edges of the crust with foil (which I neglected to do here) and bake at 400 degrees for 15 minutes, then remove foil and bake another 15 minutes or until quiche is cooked through.