Boil water and cook shells according to package directions (about 15 minutes), make sure to make them al dente.
In a large sauce pan add spaghetti sauce and italian seasoning, then simmer on low, covered for about 10 minutes.
Preheat oven to 375°F
In a large bowl, mix together ricotta, egg, spinach, mozzarella, italian seasoning, parmesan, salt & pepper.
Once shells are cooked and have cooled, fill shells with the cheese mixture and place in baking dish with a little sauce in the bottom. Cover shells with remaining sauce, cover with foil and bake 40 minutes, uncover foil and bake 5 more minutes.