Heat a large, non-stick skillet over medium. Season chicken with salt and pepper, and add to hot skillet. Cook until browned on both sides and no longer pink in the center, then remove from heat and shred.
Meanwhile, cook pasta as directed on package; drain, rinse, and set aside.
Chop pineapple, dice celery, slice onion, roughly shred spinach, and slice grapes and orange wedges into halves.
Toss all ingredients into a large bowl and stir in dressing. Serve immediately, or cover and refrigerate for later.