Cook shell macaroni according to package directions. Drain. Set aside.
For filling, in a medium mixing bowl combine spinach, feta cheese, ricotta cheese, 3 tablespoons of the walnuts, the egg white, salt, cinnamon, and pepper. Stir to mix. Set aside.
For sauce, in a medium saucepan, combine undrained tomatoes, tomato paste, water, mint, sugar, and garlic powder. Bring to boiling; reduce heat. Simmer, uncovered, about 5 minutes or until slightly thickened.
Stuff each shell with about 2 tablespoons of the spinach filling. Place in an ungreased 2-quart square baking dish. Spoon sauce over shells. Sprinkle with remaining nuts. Bake, covered, in a 350 degree F oven for 25 minutes. Sprinkle with mozzarella. Bake, uncovered, for 2 to 3 minutes more. Makes 4 main-dish servings.
Cook macaroni shells according to package directions; drain. Rinse and drain again. Place in a bowl; cover and chill up to 24 hours.