In a large bowl, mix together the flour, sugar, salt, garlic powder and thyme until combined. Cut the butter into small pieces above the bowl, stopping to stir and coat the butter bits in the flour mixture every few minutes.
Pinch the mixture together with your fingertips until it resembles the texture of damp sand. Add the water, a tablespoon at a time, mixing it with a fork, until the dough just holds together when you squeeze a fistful of it in your hand.
Combine the mixture into a ball.
Roll out the dough until it is 1/8-inch thick and transfer it to a 10-inch pie dish. Press the crust into the pan, trim off the excess leaving a 1-inch overhang, and reserve the excess dough. Fold the 1-inch overhang under the edge of the crust all the way around and pinch the edges.
Roll out the remaining dough until it is 1/8-inch thick and cut out any decorative shapes you want to place along the edge of the crust (Optional).
In a small bowl whisk together the egg with 1 tablespoon of water. Lightly brush the edges of the pie crust and place the decorative pieces along the edge, pressing down gently to adhere them with the egg wash. Lightly brush the decorative pieces with the wash.
Gently cover the pie crust with wrap and place it in the freezer for 2 hours.
For the filling, heat the olive oil over medium low heat in a large frying pan over medium heat. Add the onions and stir to coat, and cook until lightly golden and transparent, about 20 minutes, stirring regularly. Add the green onions, garlic, and soy sauce and stir to combine. Continue cooking until the garlic is softened and fragrant, about 5 to 8 minutes more, stirring often. Remove from heat and set aside.
Preheat the oven to 375 degrees Fahrenheit.
In a medium bowl, whisk together the eggs, sour cream, ricotta, milk, salt, garlic powder, oregano, and thyme until smooth.
Remove the crust from the freezer and remove the wrap. Place the pie pan on a lipped baking sheet (this will make it easier to put it in the oven). Spread the caramelized onion mixture across the bottom of the crust, then gently pour in the egg mixture. Arrange the sliced zucchini and tomatoes on top in layered concentric circles, with the wider zucchini and tomato slices around the outer edge.
Sprinkle the quiche with parmesan and bake in the oven until the edges are set but the center is *very* slightly wobbly, about 40 to 50 minutes. Remove from the oven and transfer the pie dish to a wire rack, and allow it to cool for at 30 minutes. Garnish with the fresh basil and slice and serve.