Spinach, Mushroom, & Ricotta Stuffed Shells

jumbo pasta shells (about half a 12-ounce box)

jar marinara sauce (or 3 cups homemade sauce)

part-skim ricotta

baby spinach, chopped

chopped fresh basil

chopped mushrooms

grated Parmesan (2 ounces)

kosher salt and freshly ground black pepper

grated mozzarella (4 ounces)