Rinse the zucchini and cut 8 long, thin slices. Coarsely grate the rest of the zucchini. Blanch the slices in salt water and pat dry.
Rinse the potatoes and boil in salt water for 30 minutes. Drain, peel and press through a ricer. Let the potatoes cool.
Preheat the oven to 180°C (approximately 350°F).
Peel and finely chop the onion. Saute the onion in hot butter. Let cool. Drain the quark well and place in a bowl. Separate the eggs. Mix the egg yolks, parsley, quark, parmesan, grated zucchini, onions and pressed potatoes. Carefully fold in the beaten egg whites. Season with salt, pepper and nutmeg.
Grease the edges of the ramekins and line with zucchini strips. Pour the zucchini-potato mixture into the ramekins. Bake for about 30 minutes, until golden brown. Cut the bacon into wide slices and cook in a nonstick pan until crispy. Drain the bacon on paper towels. Serve the gratin with the bacon.