Cook Manicotti according to package instructions. Drain; rinse with cool water. Let Shells dry on paper towels or wax paper.
While pasta is cooking stir together 3 C. of the shredded cheese, Ricotta, Basil & Spinach. Using a small spoon (or your fingers), carefully stuff mixture into cool pasta shells. (Be gentle! They tear easily.)
Preheat oven to 350. Spray a 13x9 or 10x14 baking dish with nonstick spray (depending on how large your shells are - I typically use the larger one so they're not too crowded).
Put 2 C. of the Marinara Sauce into the prepared baking dish. Arrange stuffed pasta over sauce. Pour the rest of the sauce over the top of the pasta. Sprinkle with remaining shredded cheese. Bake uncovered for 25 minutes.