Preheat oven to 375 degrees. Cook pasta shells according to package directions. Set aside.
Bring a large pot of lightly salted water to a boil. Add pasta shells and cook until tender yet firm to the bite, 8 to 10 minutes. Drain.
Thaw frozen spinach and squeeze out excess water.
In a medium bowl, combine the ricotta cheese, cottage cheese, spinach, parmesan cheese, spices, garlic, and egg. Stir to combine.
Spread a thin layer of marinara sauce in the bottom of a 9 x 13 pan. Stuff pasta shells with ricotta cheese mixture. Place them, open side up, in the baking dish.
Cover the top and sides of the shells with the remaining marinara. Top with mozzarella cheese.
Bake for 30 minutes, until cheese is bubbling and melted.