Preheat the oven to 350°F (175°C).
Place the manicotti shells in a large bowl and cover with hot water; soak for about 30 minutes to soften, stirring gently halfway through.
While shells soak, drain any excess liquid from the vegan ricotta and finely chop the spinach and basil.
In a mixing bowl combine the drained vegan ricotta, 1 cup of the shredded vegan mozzarella, Italian seasoning, vegan Parmesan, chopped spinach, chopped basil, cornstarch, salt, and black pepper; stir 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 corner snipped; fill each softened manicotti shell with about 1/3 cup of the mixture and arrange the filled shells in the prepared dish on top of the sauce.
Pour the remaining pasta sauce over the filled shells and sprinkle the remaining 1/2 cup shredded vegan mozzarella on top.
Cover the dish with aluminum foil and bake for 45 minutes. Remove from the oven and let rest 10 minutes before garnishing with additional basil and serving.