Add oil, celery, onion, salt and pepper. Cook, stirring frequently, until onions are translucent, 3-4 minutes.
Add broth, water, and chicken. Secure lid and turn valve to "seal." Set Instant Pot on Manual (high pressure) for 11 minutes. Quick release pressure when done cooking.
Remove chicken to a plate and turn Instant Pot back to Sauté. Add lemon juice, dill weed, garlic powder, carrots, and orzo. Continue to cook, stirring occasionally, until noodles are tender, or about 10-12 minutes (check the package for exact cooking time).
Meanwhile, shred chicken with two forks and return to pot when shredded.
When orzo has finished cooking, turn Instant Pot to warm and add spinach and stir to wilt. Taste and adjust seasoning for salt and pepper. You may also add more chicken broth or water if it's thicker than you like.
In a large stockpot or Dutch oven, heat oil over medium heat. Dice chicken and add diced chicken, celery, onion, salt and pepper. Sauté until onions are translucent, 5-6 minutes.
Add broth, water, lemon juice, dill, and garlic and bring to a boil.
When boiling, add carrots and orzo and cook for 8-10 minutes (or as your orzo package directs), until orzo is al dente. Stir in spinach until wilted, and serve!
To speed up cooking time when making the stovetop version, I recommend dicing the chicken into bite-sized pieces before adding it to the soup. You could cook it whole and shred it if that's what you prefer, but it will slightly increase the cooking time. You could also use chicken that you pull off a rotisserie chicken if you want to make this a super quick and easy recipe.