Preheat the oven to 350 degrees F. Boil the pasta shells in salted water according to the package directions. Drain once cooked.

Heat the olive oil in an oven-safe dutch oven or cast iron skillet. Add in the onion and garlic with a pinch of salt and pepper. Cook, stirring often, until slightly softened. Stir in the zucchini and squash with another pinch of salt and pepper. Cook until softened, about 5 to 6 minutes. Turn off the heat and let cool slightly.

In a large bowl, mix together the ricotta cheese, egg, 1 cup of the mozzarella cheese, the parmesan and ⅓ cup of pesto. Add in a pinch of salt and pepper. Mix until combined. Transfer the zucchini corn mixture to the ricotta and stir it in until combined.

Add the marinara sauce to the oven-safe pan that you cooked the zucchini corn mixture in.

Take each jumbo pasta shell and stuff it with 2 to 3 tablespoons of the ricotta pesto filling. Place the shells in marinara sauce in the pan. Repeat with the remaining shells. If you end up with too many shells, add some sauce in a small baking dish or pan and layer the shells in there.

Dollop the remaining pesto on top of the shells. Sprinkle with the remaining mozzarella cheese. Bake for 25 to 30 minutes, until warm and golden and bubbly.

Remove the pan and let it sit for a few minutes. Top with extra parmesan, fresh basil and even more pesto if you wish. Serve!