Season chicken with salt, pepper, paprika, and onion powder and arrange in the slow cooker.
In a medium bowl, stir condensed cream of mushroom soup, chicken broth, and minced garlic and mix until fully combined. Stir in the fresh sliced mushrooms.
Pour the mushroom sauce over the chicken. Cover and cook for 4 hours on HIGH or 6 hours on LOW.
Add the sour cream at the end of the cooking time by scooping out a little of the broth, whisking in the sour cream to warm it up, then pour it all back in to the slow cooker.
Garnish with fresh minced parsley (optional) before serving.
Notes
Slicing the chicken breasts in half (butterflying) will allow them to cook faster.Store leftovers covered in the fridge for up to 3 days.