Season chicken with salt and pepper. In large nonstick skillet over medium-high heat, brown chicken, skin side down, in EVOO, 5 to 7 minutes. Turn and brown second side, about 5 minutes. Spoon off all but 2 tbsp. fat; add celery and cover. Cook, stirring and turning chicken occasionally, until chicken is cooked through and celery is tender, about 15 minutes. Season to taste.