1) Stir the salt into the grated squash. Place the squash in a colander, weigh it down, and let it drain for an hour or so.
2) Combine the drained squash and onion. Fry in 2 tablespoons olive oil in a large skillet until soft, about 20 minutes; the vegetables will greatly diminish in volume. Season to taste with additional salt, if desired, and pepper.
3) Preheat the oven to 400°F.
4) In a large bowl, whisk together the cheese, eggs, and flour.
5) Add the cooked squash, drained of any liquid if necessary. Stir to combine.
6) Drizzle 1 tablespoon olive oil into a 9" or 10" cast iron skillet, and heat the skillet on the stovetop until the oil is very hot.
7) Spread the vegetable mixture evenly in the pan. Bake the frittata for about 20 to 25 minutes, until it's light golden brown on top.
8) Remove from the oven, and serve hot, in wedges.
Yield: 8 to 10 servings.