Thaw turkey, if frozen. Preheat oven to 400 degrees F. Coat a large shallow roasting pan and rack with cooking spray. Place turkey breast halves, bone side down, on rack in prepared pan. Set aside.
In a medium bowl combine pesto, sage, walnuts, salt, and pepper; mix well. Reserve half the pesto mixture to pass with turkey. Cover; chill until serving time.
Starting at the breast bone, slip your fingers between skin and meat to loosen skin, leaving skin attached at top. Rub about two-thirds of the remaining pesto mixture under the skin over the breast meat. Rub remaining pesto mixture over the skin of each breast halve. Insert an oven-going meat thermometer into thickest part of turkey breast, without touching bone. Roast, uncovered, for 20 minutes. Reduce oven temperature to 350 degrees F. Roast 1-1/4 to 1-1/2 hours longer or until thermometer registers 170 degrees F., juices run clear, and turkey is no longer pink. Cover with foil the last 30 to 45 minutes, if necessary to prevent overbrowning. Let stand, covered with foil, for 10 minutes before slicing. Serve with remaining pesto mixture and the Onion-Thyme Gravy. Makes 10 to 12 servings.
In a medium saucepan melt butter over medium-high heat. Add onion, shallots and fresh or dried thyme; cook, stirring occasionally, for 10 to 12 minutes or until vegetables are tender and browned. Stir in flour; cook and stir for 1 minute. Add chicken broth, soy sauce, and Worcestershire sauce. Cook and stir until mixture comes to boiling; reduce heat to medium. Simmer, uncovered, for 8 to 9 minutes or until slightly thickened. Stir in salt and pepper. Makes 2-1/4 cups or nine 1/4 cup servings.