Heat a 22cm non-stick ovenproof frying pan over high heat. Cook the bacon for 3 minutes or until golden, then remove and set aside and reduce heat to medium-high. Melt the butter in the pan. Cook the mushrooms for 5 minutes or until golden, tossing the pan regularly. Remove and set aside.
Meanwhile, stir most of the parsley and parmesan through the eggs, reserving some to serve. Season with salt and pepper.
Heat the oil in the pan over medium heat. Pour the egg mixture into the pan, then top with the bacon, mushrooms and zucchini. Cook the frittata for 4 minutes or until golden on the base.
Meanwhile, preheat the grill to high. Grill the frittata for 5 minutes or until golden. Scatter with the remaining parsley and parmesan to serve.