In saucepot, prepare pasta as label directs in boiling salted water, drain. Return pasta to saucepot.
Meanwhile, in 3-quart saucepan, heat tomato sauce, covered, until hot over medium-low heat. (If tomato sauce is frozen, add 2 tablespoons water to saucepan to prevent sorching). Add 3 cups sauce to pasta in saucepot, toss well. Reserve remaining 1 cup sauce.
In medium bowl, stir together egg, ricotta cheese, Parmesan cheese, parsley, salt, and pepper.
Preheat oven to 400 degrees F. Into 3 1/2- to 4-quart shallow casserole or 13-inch by 9-inch glass baking dish, spoon half the pasta mixture, top with all the sliced meatballs. Drop ricotta-cheese mixture by spoonfuls evenly over meatball layer. Spoon remaining pasta mixture over ricotta-cheese layer, then spoon remaining 1 cup sauce over pasta. Sprinkle with shredded mozzarella cheese.
Bake, uncovered, 60 minutes or until very hot and cheese browns slightly.