In a bowl, combine diced pepperoni, sliced black olives, chopped green bell pepper, sliced mushrooms, shredded mozzarella cheese, and chopped green onions; mix well. Spread evenly in a 9-inch unbaked pie crust.
In a bowl, combine eggs, half-and-half, salt, and oregano; mix well. Pour over the cheese mixture and bake at 375°F for 30 minutes, or until light brown. Let stand for 10 minutes before serving.