Preheat oven to 180°C. Remove spinach leaves from stems, discard stems and roughly chop leaves. Rinse well in cold water to remove dirt. Place into a bowl and cover with boiling water. Stand for 2 minutes, drain and refresh in cold water. Drain well, squeeze out excess water, and set aside. Meanwhile, cook pasta in boiling salted water for 5 minutes. Drain and set aside to cool.
Finely chop spinach and combine with ricotta, parmesan, egg and nutmeg. Season with salt and pepper. Fill pasta shells with ricotta mixture - each shell will need approximately 2 teaspoons.
Put tomatoes into a large baking dish and stir in 1 cup of water. Arrange shells over tomato mixture. Sprinkle Mozzarella over the top. Bake for 30 minutes and serve.
