Place onions, carrots, celery, mushrooms, rice, chicken, garlic, parsly, mrs. dash, bay leaves, broth, water salt and pepper into the instant pot.
Cover and cook on soup setting (or high pressure) for 35 minutes. When time is up do quick release. While steam is release, prepare the roux.
To make the roux (soup thickener), in a small sauce pan, melt butter over a medium beat. Once melted, whisk in flour. once butter and flour are well combined, slowly whisk in half and half. Once the sauce thickens (about 2-3 minutes) remove from heat.
Once pressure has released, open and remove the chicken, shred it using two forks, and add it back into the instant pot.
Stir the prepared roux into the instant pot and let sit for 5-7 minutes before serving. And adjust salt and pepper as desired.