Preheat oven to 350 degrees. Put all the marinade/dressing ingredients in a blender and mix thoroughly at low speed.
Place the chicken in a shallow baking dish. Pour half of the mixture from the blender over the poultry, reserving the remainder. Cover and refrigerate the chicken for 20 minutes.
While the chicken is marinating, bring a large pot of water to boil over high heat. Add the fettucini and cook for 8 to dozen minutes, to desired doneness.
In the meantime, remove the chicken from the refrigerator. Uncover the baking dish and transfer it to the oven. Bake for 15 minutes, until the meat is no longer pink and the juices run clear.
When the pasta is cooked, remove the pot from the heat. Drain the fettucini and return it to the pot. Stir in the chicken stock and keep the mixture warm over the lowest heat setting. Pour the cooking juices from the chicken into a saute' pan. Add the squash, bell pepper, leek, broccoli and mushrooms. Saute for about 3 minutes, just until the vegetables begin to wilt.
Transfer the pasta to a warm serving bowl, along with the vegetables. Shred the chicken on top. Add the reserved dressing and toss. Garnish with the snipped chives.