Remove the lid from a 3-quart Instant Pot and turn on the Sauté setting. (See your manufacturer's guide for detailed instructions on how to use your Instant Pot). Add the oil and once hot add the onions, carrots, celery, and garlic. Season the vegetables with salt, pepper, and Italian seasoning. Cook, stirring occasionally until the vegetables are slightly softened, 4-5 minutes.
Add the chicken, green beans, and chicken broth. Turn off Sauté function by pressing Cancel. Secure the lid on the Instant Pot, and turn the valve on top to Sealing. Set to Pressure Cook on High for 15 minutes.
After the pressure cook cycle is complete the Instant Pot will beep. Use the natural release cycle to allow the cooker to cool naturally. This should take about 10 minutes. You may also follow the manufacturer's guide for quick release. When the valve drops, it is safe to open the Instant Pot. Unlock and remove the lid.
Press the Sauté setting again. When the soup begins to boil, add the noodles to the pot and cook until al dente, 4-5 minutes.
While the noodles are cooking, use two forks and shred the chicken into bite-size pieces.
When the noodles are done, press Cancel on the Instant Pot. Season the soup with additional salt, if necessary. Ladle the soup in a bowl and enjoy immediately.
Notes
Expert Tips
Mind the Quick-Release: Exercise caution when performing the quick-release on your Instant Pot, especially with soups or recipes containing a lot of liquids. This step can release a substantial amount of steam after cooking.
Natural Pressure Release Option: If you prefer to avoid the quick-release, you can patiently wait for the pressure to release naturally. It's a safer option that doesn't compromise the quality of the dish.