Toss grated zucchini with the 2 tsp. sea salt and allow it to sit for 30 minutes, exuding its water.
Preheat the oven to 375 degrees (about 10 minutes before the zucchini's done sitting).
Place the eggs, kale and garlic in a blender.
Blend for 15 seconds on low speed, or just until the kale is in small even pieces, with no large leaves remaining. Use the pulse button as needed.
Add the cream and remaining sea salt. Process briefly to mix, 5 to 10 seconds.
Drain the grated zucchini in a colander and rinse it well.
Squeeze out any excess liquid.
Place the grated zucchini, 2 cups of cheddar and Parmesan cheese in a medium size bowl and toss to mix thoroughly.
Grease large casserole dish or cast iron skillet.
Pour the grated zucchini and cheese into the dish and spread it out evenly.
Pour the kale egg custard over the zucchini.
Bake the crustless quiche for 25 minutes. Remove from oven and top with raw zucchini slices, spreading them over the top of the casserole. Bake another 15 minutes. Briefly remove the casserole from the oven one last time. Top the casserole with reserved final 2 cups of grated cheese.
Bake an additional 20 minutes.
The dish will be puffed and gorgeous but will deflate a little before you serve.
Allow casserole to cool for 5 to 15 minutes before serving.
Serves 10 or more, especially if you have side dishes.