Heat a large pot of water until boiling. Cook the jumbo shells until al dente as per package direction, approximately 10 minutes. Drain and set aside.
In a small bowl, combine the pesto sauce with 1/3 cup of heavy cream. Add additional cream or water until you get a sauce that is your desired creaminess and consistency, keeping in mind that the sauce will thicken as it bakes in the oven. (You could also substitute cream and water for milk).
While the pasta is cooking, combine all of the cheese mixture ingredients and set aside. (Zest the lemon into the cheese mixture, then juice. For a heavy lemon flavor, use two full lemons).
Also while the pasta is cooking, heat a large non stick skillet with 2 Tablespoons of oil. When hot, add the diced zucchini and a sprinkle of salt and pepper. Cook until the zucchini is tender, approximately 5-7 minutes. Set aside.
Heat the oven to 375 F.
When everything is ready, combine the zucchini in the cheese mixture and mix.
Place a little of your sauce in the bottom of your baking dish to cover. Using a spoon, scoop approximately 1.5-2 Tablespoons of the cheese mixture into each shell. Place the shell in the baking dish, open side up.
Repeat with the remaining cheese mixture and shells.
Cover the shells with the creamy pesto sauce, 3/4 cup mozzarella, and 1/4 cup Parmesan cheese. Add more or less sauce and cheese as desired. Bake at 375 F until the cheese is melted and starting to brown on top, approximately 20 minutes.
Garnish with additional fresh basil if desired and serve immediately.
The exact number of shells will vary based on how much you stuff them.You can use any pesto sauce, but I love my homemade pesto recipe which you can find here. One batch is the perfect amount for this recipe.To ensure a truly vegetarian dish, ensure you are using vegetarian cheeses.