Finely grate the zucchini into a colander, sprinkle with salt, mix well and allow to drain for 30 minutes. Rinse under running water and squeeze dry with your hands, then place in a clean dish towel and squeeze again.
Transfer the zucchini to a bowl and add the egg, matzo meal, nutmeg, and pepper to taste. Mix together until well combined, then allow to stand for 20 minutes for the flavours to develop.
To make the sauce, combine the lemon zest and juice, mint and yogourt in a bowl, then cover and chill until ready to serve.
Heat a ridged cast-iron grill pan or nonstick frying pan over medium heat. Place tablespoons of the zucchini mixture onto the pan, flattening each to form a thick cake. Dry-fry the cakes for 4-5 minutes on each side, until they are firm and browned. (You may need to cook them in two batches.) Garnish with the mint and serve hot, with the chilled sauce on the side.
Each serving: 8 g protein, 3 g fat of which 1 g saturates, 18 g carbohydrate, 2 g fibre, 129 Calories