1. Preheat your oven to 375 F (190 C). In a medium bowl, toss the diced zucchini, yellow squash, red bell pepper, cherry tomatoes, and chopped red onion with olive oil. Spread the vegetables in a single layer on a baking sheet.

2. Place the baking sheet with the vegetables into the preheated oven. Roast for 10-12 minutes, or until the vegetables are tender-crisp and slightly browned. Remove from the oven and set aside to cool slightly.

3. While the vegetables are roasting, unroll your store-bought sourdough pie crust and carefully press it into a 9-inch pie plate. Crimp the edges decoratively if you wish. Prick the bottom of the crust several times with a fork.

4. In a large bowl, whisk together the eggs, half-and-half (or milk), salt, pepper, and dried thyme until well combined and slightly frothy.

5. Sprinkle half of the shredded Gruyere cheese evenly over the bottom of the prepared pie crust. Then, arrange the roasted vegetables over the cheese in the pie crust. Pour the egg mixture evenly over the vegetables and sprinkle the remaining cheese on top.

6. Carefully transfer the pie plate to the preheated oven. Bake for 40-45 minutes, or until the center is set and the top is golden brown. To check for doneness, gently shake the pie plate; if the center jiggles only slightly, it’s ready. A knife inserted near the center should come out clean.

7. Once baked, remove the quiche from the oven and let it cool on a wire rack for at least 10-15 minutes before slicing and serving. This cooling period allows the custard to fully set, making for cleaner slices.