Add liquid ingredients, Italian seasoning and garlic powder to slow cooker. Stir and make sure all is distributed evenly.
Add chicken breast and keep cover by the liquid.
Add potatoes, carrots, mushroom and onion. Mix well
Cook for 7 hours on high heat – add cornstarch about 30 minutes before serving (I pulled a separate amount of liquid out, mix it, and then returned it to crockpot to avoid clumps)