Set the Instant Pot to sauté mode and add a splash of oil. Once hot, add diced onions, carrots, and celery. Cook, stirring occasionally, until fragrant and vegetables are slightly softened, about 5 minutes.
Add the chicken breasts on top of the sautéed vegetables, then pour in the broth. Sprinkle with herbs, salt, and pepper.
Seal the lid and set the Instant Pot to high pressure for 10 minutes. Ensure the valve is set to sealing.
Once the cooking cycle finishes, allow natural pressure release for 10 minutes, then carefully turn the valve to vent to release remaining pressure.
Open the lid and check that the chicken is cooked through and tender. Remove the chicken and shred it with two forks.
Return the shredded chicken to the soup, then add noodles or rice if using. Set the Instant Pot to sauté mode again and cook until noodles or rice are tender, about 5 minutes.
Squeeze fresh lemon juice into the soup for brightness and stir to combine. Taste and adjust seasoning with salt and pepper as needed.
Let the soup sit for a minute or two to meld flavors, then ladle into bowls and serve hot, garnished with extra herbs if desired.
