First prepare the chicken. This can be done ahead of time, if desired. Bring a large pot of water seasoned with celery salt and onion salt to a boil. Add chicken breasts and let boil/simmer 15 minutes or so until cooked through. Remove chicken and allow to cool, then shred. (I put the chicken breasts in my kitchen-aid mixer with the paddle attachment and turn on to low to let it shred the meat for me.) 

Chop celery, halve grapes, chop pecans, and add them to the shredded chicken. 

Chop the fresh dill and dice the green onion (I discard the white part and very tip of the green, then dice the rest) and place them in a large bowl. Add mayonnaise, sour cream, black pepper, salt and the juice of one small lemon, and stir well.

Dump the shredded chicken mixture into the dressing and stir to combine.

For best flavor, cover and refrigerate 6 hours or overnight. Can be eaten plain or put in croissants for a lovely sandwich.