Preheat the oven to 350°F (175°C).
Place the manicotti shells in a large bowl and cover with very hot water; soak about 30 minutes until softened, stirring gently halfway through.
While the shells soak, drain any excess liquid from the vegan ricotta.
In a mixing bowl combine drained vegan ricotta, 1 cup of the shredded vegan mozzarella, Italian seasoning, vegan Parmesan, chopped spinach, chopped basil, cornstarch, salt, and black pepper; mix until well blended.
Lightly spray a 9×13-inch baking dish with nonstick spray and spread half of the pasta sauce evenly over the bottom.
Transfer the cheese mixture to a piping bag or a zip-top bag with a snipped corner and pipe about 1/3 cup of filling into each softened manicotti shell, then arrange the filled shells seam-side down in the baking dish on top of the sauce.
Pour the remaining pasta sauce over the arranged shells and sprinkle the remaining 1/2 cup shredded vegan mozzarella evenly on top.
Cover the dish with aluminum foil and bake for 45 minutes.
Remove from the oven and let rest 10 minutes, then garnish with additional basil if desired and serve.
