CUT enough of the basil into thin slices to measure 2 Tbsp.; set aside. Place remaining basil in blender container. Add 1/4 cup of the walnuts, 1/3 cup of the chicken broth and the garlic; cover. Blend 30 to 1 min. or until smooth.
COOK pasta according to package directions. Meanwhile, heat oil in large skillet on medium-high heat. Add chicken, broccoli and peppers; cook and stir 5 min. or until chicken is lightly browned. Add remaining 1/3 cup broth; cook an additional 6 to 8 min. or until chicken is cooked through and vegetables are crisp-tender, stirring occasionally.
DRAIN pasta. Add to ingredients in skillet along with the basil sauce; stir until well blended. Drizzle with the vinegar; mix lightly. Sprinkle with the reserved sliced basil and remaining 1/4 cup walnuts.