When draining the spaghetti, reserve 1/4 cup of the cooking water to toss with the spaghetti and pesto, if necessary, if the mixture seems dry.
To toast walnuts, sprinkle in ungreased heavy skillet. Cook over medium heat 5 to 7 minutes, stirring frequently until nuts begin to brown, then stirring constantly until nuts are golden brown.
Use your favorite variety of whole wheat or multigrain pasta in this recipe. Penne or bow-tie (farfalle) would also work great.