Preheat oven to 350 degrees F. Cook pasta according to package directions; drain and set aside.

Meanwhile, for filling, drain thawed spinach well, pressing out excess liquid. In a medium bowl combine spinach, feta cheese, ricotta cheese, walnuts, egg white, cinnamon, and pepper; set aside.

For sauce, combine undrained tomatoes, tomato paste, mint, sugar, and garlic. Stuff each pasta shell with 2 slightly rounded tablespoons of the spinach filling. Arrange filled pasta shells in an ungreased 2-quart square baking dish. Spoon sauce over shells. Bake, covered, for 30 to 35 minutes or until heated through. Sprinkle with mozzarella cheese. Bake, uncovered, for 2 to 3 minutes more or until cheese is melted. Makes 6 (2-shell) servings.