To prepare salad, cook pasta according to package directions, omitting salt and fat. Drain; rinse with cold water. Combine pasta, chicken, tomatoes, and olives in a large bowl.
To prepare walnut pesto, combine basil and next 6 ingredients (through garlic) in a food processor; pulse 6 times or until finely minced. Add pesto to pasta mixture, tossing gently to coat. Place 1 lettuce leaf on each of 4 plates; top each serving with salad mixture.