In a bowl, combine the drained vegan ricotta, 1 cup of the vegan mozzarella, Italian seasoning, vegan Parmesan, chopped spinach, basil, cornstarch, salt, and pepper.
Transfer the vegan cheese mixture to a piping bag (or zip-top bag with a snipped corner) and fill each softened manicotti shell with 1/3 cup of the mixture.
After all shells are filled, pour the remaining pasta sauce over them and sprinkle the remaining 1/2 cup of vegan mozzarella cheese on top.