Preheat oven to 375°F (190°C).

Prepare the Crust:
In a large bowl, whisk together flour and salt.
Cut in the cold butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs.
Gradually add ice water, 1 tablespoon at a time, mixing until the dough just comes together.
Form the dough into a disc, wrap in plastic wrap, and chill for at least 30 minutes.
On a lightly floured surface, roll out the dough into a 12-inch circle.
Carefully transfer the dough to a 9-inch pie plate, pressing it into the bottom and up the sides.
Trim and crimp the edges as desired.
Prick the bottom of the crust with a fork.
Line the crust with parchment paper and fill with pie weights or dried beans.
Blind bake for 15 minutes. Remove parchment and weights, and bake for another 5-7 minutes until lightly golden.

Prepare the Filling:
While the crust is baking, heat olive oil in a skillet over medium heat.
Add diced zucchini and chopped onion (if using) and sauté until tender, about 5-7 minutes.
Stir in the sweet corn and cook for another minute.
In a separate bowl, whisk together eggs, milk, salt, pepper, and nutmeg.

Assemble and Bake:
Sprinkle the sautéed zucchini and corn mixture evenly over the bottom of the pre-baked crust.
Sprinkle the shredded cheddar cheese over the vegetables.
Pour the egg and milk mixture over the cheese and vegetables.
Bake for 25-30 minutes, or until the center is set and the top is golden brown.
Let the quiche cool for at least 10 minutes before slicing and serving.