Press tofu to remove excess water. Wrap the drained block of tofu with a clean kitchen towel or a couple layers of paper towel. Place a heavy pan on top with some books. Press tofu for 15-20 minutes.
Cook the jumbo shells according to box instructions. Drain and rinse well. Set aside.
Preheat oven to 400 degrees F. After the tofu is done being pressed, crumble it with your hands into a large mixing bowl. Add the hummus, nutritional yeast, garlic powder, salt, pepper, and lemon juice. Mix well until it resembles ricotta cheese. Chop blanched spinach and fold it into the mixture. Make sure everything is well combined. Taste and adjust seasonings if needed, adding more salt or pepper.
Spray a large casserole dish (9×13) and pour enough marinara sauce to cover the bottom. Fill the shells with about 1.5 to 2 tablespoons of the tofu ricotta. Place in the casserole pan. Once you finish filling the shells, about 24 shells, pour the rest of the sauce over the shells. Cover the dish with foil and bake for 15 minutes. Then take foil off and lower temperature to 375 degrees F and bake for another 10-15 minutes.
Remove from oven and serve. Enjoy!