On the water, stew the chopped onion, add the minced meat, salt, thyme, pepper and grated celery and stir until the meat gets brownish color. Stir and remove from cooker. In another pan (ovenproof dish) on the bottom line up zucchini slices 3-4 mm thick, and the gaps between the rings fill with the chopped zucchini cut into cubes. Pour over meat and put another layer of zucchini. In the pan in which the meat is fried, whisk 1 egg and 2 egg whites, add 200 ml of yogurt and water to the end and pour the mixture of squash and meat. Moussaka furnace in the oven at 300 ° C until the surface appears brownish crust (if you prepare it just for you, you can make a small amount and put only one egg). This moussaka can be prepared with cauliflower, roasted peppers and other vegetables.