Grate the zucchini (you may have to peel it if the zucchini is very large and the skin has become woody) and squeeze the excess water from the spinach.

Toss the grated zucchini with about a teaspoon of salt. Place the grated zucchini in a large sieve (or colander) placed over a bowl to catch the water as the salt helps the zucchini release its moisture. Let sit for 30 minutes or so, then squeeze out the remaining excess moisture with paper towels or a clean tea towel.

Sauté onions in oil for about 10 minutes, or until the onions have softened.

Meanwhile, place the parsley and garlic with a small pinch of salt into a food processor and pulse just a couple of times.

In a large bowl, combine zucchini, onions, spinach, parsley, and garlic. Mix in half of the Parmesan. Taste, and add black pepper and more salt if needed. Mix in the eggs. Grease the bottom and sides of a 2 quart casserole or gratin dish with a tablespoon of olive oil. Put the mixture into the dish and pack it down.

Sprinkle the remaining Parmesan cheese over the top and drizzle with a little olive oil, bake in oven at 350°F until top is browned.