Substitute any mushroom for the shiitakes.
Sauté onion and mushrooms in hot oil in a large skillet over medium heat 15 minutes or until tender.
Stir together eggs and next 5 ingredients in a large bowl; stir in onion mixture. Spoon mixture into pastry shell, and place on a baking sheet.
Bake on lower oven rack at 350° for 45 minutes or until done.
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