Cook pasta shells according to package directions. Drain and set aside.

In a large bowl, combine ricotta cheese, spinach, Parmesan cheese, parsley, egg, salt, and pepper.

Preheat oven to 375°F (190°C).

Spread a thin layer of marinara sauce in the bottom of a 9x13 inch baking dish.

Stuff each pasta shell with the ricotta mixture and arrange in the baking dish.

Pour the remaining marinara sauce over the stuffed shells.

Bake for 25-30 minutes, or until bubbly and heated through.