Add all of the ingredients except ice water to the bowl of a food processor. Pulse until coarse crumbs are formed.
With the machine running, pour the ice water down the feed tube and pulse the machine until the dough begins to form a ball. Wrap in plastic wrap and refrigerate while you prepare the filling. At least 30 minutes.
After 30 minutes, roll the dough and fit to your desired pan. Dock with a fork and return to the refrigerator.
TO PAR-BAKE THE PIE CRUST:
To par-bake a crust that will be baked again later: Bake at 400° F until the crust just begins to brown (it will still be pale, but it should not look like raw dough). This time may vary based on your oven and your pie plate, but should take around 15 to 20 minutes.
TO PREPARE THE FILLING:
Preheat oven to 400 degrees.
In a saute pan, add the oil, scallions and onion. Saute until the onions are translucent. Add the garlic and saute for just 1 minute more. Remove from heat.
Meanwhile, add the sliced zucchini and yellow squash to a microwave safe bowl and cook for 3-4 minutes or until the squash is par-cooked.
Par-cook the corn and pearl onions in the same manner.
Add the cooked onions to the bottom of the pie dough and top with a layer of the vegan mozzarella and vegan parmesan.
Layer the zucchini and yellow squash. Top with the corn and pearl onions.
Finish with another layer of each of the two cheeses and parsley (or other herbs as desired). Season with salt and pepper.
Bake for about 30-40 minutes or until the crust is golden and the squash tender.