Cook pasta according to package directions; drain.
Stir together chicken and next 6 ingredients.
Cut pasta shells lengthwise through the other side. Spoon about 1/2 cup chicken mixture into each shell, gently pressing cut sides together. Place, cut sides down, in 2 lightly greased 11- x 7-inch baking dishes.
To make Roasted Red Pepper sauce, combine Alfredo sauce, roasted red peppers and Parmesan cheese in a food processor. Pulse until smooth.
Pour Roasted Red Bell Pepper Sauce evenly over shells. Bake, covered, at 350° for 25 to 30 minutes or until thoroughly heated. Garnish, if desired