Place spinach with rinsing water still clinging to the leaves in a large saucepan. Cover and cook over high heat, 3 minutes. Shake the pan often. Drain, set aside to cool.
Combine zucchini, half the garlic and all the stock in the same pan. Bring to the boil; boil just until tender, 3 minutes. Place mixture from pan, half the ricotta, the walnuts, 2 tbsp parmesan and salt and pepper to taste in a food processor. Purée until smooth.
Squeeze spinach dry and chop coarsely. Mix spinach with marjoram, chives, basil, the remaining garlic and ricotta and the egg in a medium bowl.
Preheat oven to 190ºC. Stuff pasta with spinach mixture. Arrange in baking dish. Pour zucchini sauce over the top and sprinkle with remaining parmesan. Cover. Bake for 30 minutes. Sprinkle on edam. Let stand 5 minutes before serving.