1. Prepare the Chicken: Start by placing the boneless, skinless chicken breasts or thighs at the bottom of your slow cooker. You can leave them whole or cut them into 1-inch pieces if you prefer smaller chunks in your casserole.

2. Combine the Liquids and Seasoning: In a medium bowl, whisk together the cream of chicken soup, cream of mushroom soup, chicken broth, milk, black pepper, and garlic powder until well combined and smooth. This creates the rich, creamy base for your casserole.

3. Add Rice and Vegetables: Pour the contents of the wild rice mix (the rice and the seasoning packet) over the chicken in the slow cooker. Scatter the chopped yellow onion and the frozen peas and carrots blend evenly over the rice.

4. Pour Over the Creamy Mixture: Carefully pour the whisked soup and broth mixture over all the ingredients in the slow cooker, ensuring everything is well covered. Do not stir at this stage; let the liquid seep down naturally.

5. Cook to Perfection: Cover your slow cooker with the lid. Cook on the LOW setting for 6-8 hours, or on the HIGH setting for 3-4 hours. The chicken should be very tender and easily shreddable, and the wild rice should be fully cooked and soft.

6. Shred and Stir: Once cooked, remove the chicken from the slow cooker and shred it using two forks. Return the shredded chicken to the slow cooker. Stir everything together gently to combine the chicken, rice, vegetables, and creamy sauce.

7. Rest and Serve: Allow the casserole to rest, uncovered, for about 10-15 minutes in the slow cooker. This resting period allows the sauce to thicken slightly. Garnish with fresh chopped parsley if desired, and serve warm.