Heat oven to 400 degrees F.
Bring your store-bought pie crust to room temperature.
Start by dicing the zucchini (I cut mine into half moons, then cut those in half too). Set aside. Remove the husks and silks of the corn and slice the kernels off the cob as well. Set aside. While you're at it, chop up some fresh basil leaves (I chiffonade mine). Set aside.
In a medium sized pan, heat some olive oil on medium-high heat.
Add in the whole cherry tomatoes. Let them burst and release their juices.
Add in the diced zucchini and leave it to soften in the tomato juices for 3-4 minutes.
Once softened, toss in the fresh corn, grated Parmesan cheese and most of chopped basil (save the rest for topping the galette later). Season the mixture with salt and pepper.
Mix everything together to distribute everything evenly and let the cheese melt. Then set aside to cool for a few minutes.
Lay out a sheet of parchment paper on a baking sheet and unroll your store-bought pie crust right on top.
Spoon the vegetable filling into the center of the pastry. Make sure you leave a 2-inch border on all sides.
Fold over the dough edges, overlapping one side over the next.
In a small bowl, whisk up the egg. Using a pastry brush, brush pastry with the egg.
Evenly sprinkle everything but the bagel seasoning all over the edges of the crust as well as a little more Parmesan cheese for good luck!
Bake for 30-40 minutes. The edges of crust should be golden brown and the roasted vegetables in the center should be bubbling.
Top with the reserved basil and let cool for at least 15 minutes before slicing.