Set pressure cooker to "sear", add oil, and press "start/stop". When hot, add leeks and celery. Cook until tender. Add chicken, orzo, and stock. Season with sea salt and fresh ground black pepper.
Close and lock lid, set pressure cooker to "poultry", and adjust time to 10 minutes. Press "start/stop". When done, quick release and make sure all pressure is released before opening lid.
Carefully open lid and remove chicken. Shred chicken with a fork and return chicken to cooker. Add fresh dill. Squeeze half a lemon into to each bowl, catching the seeds. Serve hot.