Cook the shells according to the package instructions. Tip: cook an additional 3 or 4 shells just in case some break apart.
Preheat the oven to 375℉.
Drain the tofu. Then blend the tofu with the cashews, lemon juice, garlic powder, parsley, salt, and pepper until a similar texture to ricotta cheese. I prefer to use a food processor but a regular blender will work fine (you may need to scrape down the sides.) Fold in the basil.
Spread 2 cups of the sauce into the bottom of a 9x13 dish.
Stuff each shell with the vegan ricotta mixture and place in the dish. Top with remaining marinara sauce. Add vegan mozzarella on top if desired.
Cover the dish with foil and bake for 30 minutes.
To chiffonade basil, stack the leaves on top of each other, then roll up tightly. Slice into strips with a sharp knife.