Preheat oven to 400ºF.
Place chicken breasts on a sheet pan lined with foil. Drizzle olive oil over both sides of the chicken breasts, rubbing to coat evenly. Season generously with salt, pepper, and dried dill. Roast chicken until a meat thermometer reads 165ºF, about 20–25 minutes. Let chicken rest for 10 minutes.
Transfer cooked chicken to the bowl of a KitchenAid mixer and carefully pour in any accumulated juices from the sheet pan. Quickly shred the chicken using the mixer’s paddle attachment, or alternatively, shred by hand in a large bowl, using two forks.
In a large serving bowl, combine yogurt, mayonnaise, celery, scallions, lemon zest and juice, and fresh dill. Stir until mixed; taste and season with salt and pepper. Add in the shredded chicken and stir until well combined. Refrigerate chicken salad until ready to eat; serve on sandwiches or with lettuce and crackers.
