1. Preheat your oven to 375 F (190 C). Unroll the sourdough crescent roll dough and press it into a 9-inch pie plate, sealing any seams to form a solid crust. You want it to cover the bottom and sides evenly.

2. In a medium skillet, heat the olive oil over medium heat. Add the chopped zucchini, yellow squash, bell pepper, and red onion. Saute for about 5-7 minutes, or until the vegetables are tender-crisp and slightly softened. This step helps to remove excess moisture and concentrate their flavors.

3. In a medium bowl, whisk together the eggs, milk, shredded Parmesan cheese, salt, and black pepper until well combined. The mixture should be smooth and slightly frothy.

4. Spread the sauteed vegetables evenly over the bottom of the prepared crescent roll crust in the pie plate.

5. Carefully pour the egg mixture over the vegetables in the pie plate. Gently shake the pie plate to ensure the egg mixture settles evenly around the vegetables.

6. Place the quiche in the preheated oven and bake for 20-25 minutes, or until the crust is golden brown and the center of the quiche is set. You can test for doneness by inserting a knife into the center; if it comes out clean, it’s ready.

7. Remove the quiche from the oven and let it cool for 5-10 minutes before slicing and serving. This allows the quiche to set further and makes for cleaner slices.