Spray the inside of your slow cooker with nonstick spray. Add the chopped onions and chicken thighs (or breasts).
In a small bowl, stir together the cream of chicken soup, paprika, salt, and black pepper. Pour this mixture over the chicken and onions in the slow cooker.
Cover and cook on low for 5 to 7 hours, or until the chicken is fully cooked and the onions are tender.
Once cooked, remove the chicken and keep it warm.
In a bowl, mix 1 cup of the hot liquid from the slow cooker with the sour cream. Stir the sour cream mixture back into the slow cooker.
If you’d like a thicker sauce, stir in your chosen thickener (cornstarch slurry or xanthan gum mixture). Cook uncovered on low for a few more minutes until thickened to your preference.
Return the chicken to the slow cooker and coat it in the sauce, or serve the sauce poured over top.
Serve hot over egg noodles, mashed potatoes, riced cauliflower, or roasted vegetables. Garnish with parsley or green onions if desired.