Add your chicken to the slow cooker. Season well with salt and pepper.
Mix the hot water and chicken base to a small bowl and mix until the base is dissolved. You may also just use chicken broth, but the base adds a richer flavor.
To the slow cooker, add the chicken broth mixture you just made, wild rice, garlic powder, veggies, bay leaves, and seasonings. Cook on low for 6 hours.
Remove the chicken and shred it. You may use two forks to shred the chicken. Or, place it in the stand of your electric mixer and use the paddle attachment to shred the chicken. Add it back to the crockpot.
Add the mushrooms to the slow cooker and cover. While this is cooking, make your roux.
To make the roux, add the butter to a large skillet over medium heat. Stir it constantly.
Once it's melted, add in the flour and whisk it until a paste forms. Slowly add in your milk and half and half while whisking. Allow the roux to gently bubble and it will thicken after about 3-5 minutes.
Once your roux is thickened, add it to the slow cooker. Stir it well and let the soup cook for another 20-30 minutes.
Enjoy!