Cook the pasta in boiling salted water until al dente, drain, rinse and drain. Put in a salad bowl, pour the dressing over the warm pasta, mix well and let cool.
Mix the mayonnaise, pesto and sour cream and season with salt and pepper
Cut the chicken into bite-sized pieces, cut the celery diagonally into fine slices, save the greens for the garnish. Put some grapes aside for the garnish, halve and core the rest. Cut the carrots into fine sticks.
Add the meat, celery, grapes, carrots and pesto mayonnaise to the pasta and stir in well. Season to taste with salt and pepper.
Arrange the salad on two plates and garnish with the retained grapes and the celery greens.