Preheat oven to 400 degrees. In heavy skillet, Saute the onion in the butter over medium heat until they are clear and tender, about 5 minutes. Add tomato sauce, garlic, salt, pepper and oregano. Bring mixture to a boil; reduce heat and simmer 10 to 15 minutes or until mixture thickens. Set aside to cool. In a separate bowl, beat the eggs. Add olives, parsley and cayenne, stirring until well blended. Slowly fold in the tomato mixture. (Be careful. If tomato mixture is too hot, the eggs will cook and quiche will not puff.) If you wish you can make the quiche to this point and refrigerate mixture a few hours until you are ready to bake, but you have to add 10 to 15 minutes to baking time. Pour the mixture into the shell. Layer the mushrooms and any other toppings desired on top of mixture. Then sprinkle the grated cheese over the toppings. Bake in preheated oven 30 to 35 minutes (40 to 50 minutes if refrigerated) or until puffed and brown on top. Remove from oven and allow to cool 5 minutes before slicing. If you use aluminum disposable pie tin, be very careful moving quiche into and out of oven or quiche will take a dive for your kitchen floor.