Lightly coat a 5-quart or larger slow cooker with nonstick spray.

In a large nonstick pan over medium-high heat, warm about 2 tablespoons of olive oil. Add diced carrots, celery, potato, and onion, stirring occasionally for 8–10 minutes until the vegetables soften and become fragrant.

Stir in the poultry seasoning, kosher salt, and black pepper, cooking for an additional 30 seconds before transferring the mixture to the slow cooker.

Rinse the wild rice thoroughly under cold water, then add it directly to the slow cooker with the sautéed vegetables.

Arrange the trimmed boneless skinless chicken breasts on top of the wild rice and vegetable mixture. Pour in 4 cups of low-sodium chicken stock.

Cover the slow cooker and set it to cook on low for 6–7 hours or high for 2.5–3.5 hours.

Once cooking time is complete, remove the chicken and shred it into bite-sized pieces, then return to the pot.

In a separate saucepan over medium heat, melt 4 tablespoons of unsalted butter. Whisk in an equal amount of all-purpose flour.

Gradually add in the milk while continuing to whisk until the mixture thickens, about 4 minutes.

Pour the prepared roux into the slow cooker, stirring well. Adjust the consistency with more chicken stock or milk as needed.