For the parsley pesto: Preheat the oven to 350 degrees F. Put the almonds on a small baking sheet and roast until fragrant and golden brown 10 to 12 minutes. Cool.
Put the almonds and parsley in a food processor and pulse until finely chopped. Add the olive oil, Parmesan and fine salt and process until smooth. Set aside.
For the frittata: Halve the leeks lengthwise and then cut crosswise into 1/2-inch pieces; you should have about 4 cups of sliced leeks. Put the leeks in a colander and rinse really well under cool water, checking for dirt between the layers. Drain well.
Preheat the oven to 300 degrees F. Spray a 9- by 13-inch baking dish with nonstick cooking spray. Coat a 10-inch skillet with 2 tablespoons of the olive oil and put over medium heat. When the oil is hot, add the leeks, garlic and thyme. Cook, stirring occasionally, until the leeks are tender but not brown, about 10 minutes. Season with some salt and pepper. Spread the leek mixture evenly in the baking dish.
Add the remaining 1 tablespoon olive oil to the skillet and return it to medium heat. Add the zucchini and cook, stirring occasionally, until tender, 5 minutes. Season with some salt and pepper. Spread the zucchini on top of the leeks.
Whisk the eggs, ricotta and parsley pesto in a large bowl until blended. Season with some salt and pepper. Pour the egg mixture over the vegetables in the baking dish and gently stir with a wooden spoon so the egg mixture is fully incorporated into the vegetables.
Put the baking dish into a larger roasting pan and pour hot water into the roasting pan to come halfway up the sides of the baking. Bake the frittata for 50 minutes; gently shake the pan, and if it still appears loose in the center, bake until it is set and only slightly jiggly in the center, about 5 more minutes.
Remove the frittata from the water bath and let it rest for 15 minutes at room temperature. Cut into squares and serve.