Using pastry according to package directions, ease into a 9-inch tart pan with a removable bottom. Press pastry into flutes on the side of the tart pan and trim even with top of pan. Do not prick. Line pastry with a double thickness of foil. Bake in a 450 degree F. oven for 8 minutes. Remove foil; continue baking for 4 to 5 minutes or until set and dry. Reduce oven temperature to 375 degrees F.
Meanwhile, in a large skillet cook shiitake mushrooms, brown or white mushrooms, oyster mushrooms, and the 1 teaspoon marjoram in margarine or butter over medium-high heat for 4 to 5 minutes or until mushrooms are tender and any liquid is evaporated. Remove from heat.
In a large bowl combine Gruyere cheese, Swiss cheese, and the chopped Canadian-style bacon. Add mushroom mixture, eggs, milk, and chives. Stir to thoroughly mix. Pour carefully into partially baked pastry shell. Bake in the 375 degree F. oven about 20 minutes or until set and golden. Cool in pan on a wire rack for 10 to 15 minutes. Remove from pan. Cut into wedges. If desired, garnish with Canadian-style bacon wedges and additional marjoram. Makes 10 appetizer servings.