1. For the crust: Preheat oven to 350F. Grate the sweet potato.
2. Layer the bottom and sides of a quiche pan or 8x8 inch baking dish with shredded potato.
3. Bake the potato-lined dish for 20 minutes while you prepare the other ingredients.
4. For the filling: Peel and dice the onion. Slice the zucchinis thinly.
5. Heat the oil in a large, deep skillet over medium high heat. Add the onions, zucchini, and mushrooms. Sauté until the veggies are soft, 5-10 minutes. Remove from heat.
6. When crust is done cooking, remove from oven. Using a spatula, press the crust back into the sides (the sides tend to sink a bit when baking).
7. Distribute the zucchini mixture to your baked quiche crust evenly. Arrange the top so the zucchini slices lay flat and look nice.
8. Using a wire whisk, beat eggs with water. Add the basil, oregano, and salt. Stir once to combine. Gently pour beaten eggs evenly over baking dish contents.
9. Bake quiche for 30 minutes or until set.
10. Serve immediately or warm later in the oven.