Spray a 6 quart slow cooker/crockpot with non-stick cooking spray.
Cut large boneless, skinless chicken breasts in half lengthwise. Season top of chicken with 1/2 of the seasonings (salt, black pepper, garlic powder, onion powder, thyme, Italian seasoning, smoked paprika).NOTE: Season as much or as little as you want., It adds the flavor to the dish. In a large skillet over medium high heat bring oil & butter to a sizzle. Place seasoned chicken into hot skillet seasoned side down.
Season the unseasoned side with the rest of seasonings (salt, black pepper, garlic powder, onion powder, thyme, Italian seasoning, smoked paprika).
Cook chicken for 3 minutes or until chicken is golden brown on the bottom. Flip chicken over and cook an additional 3 minutes until golden brown. Remove chicken and place into prepared slow cooker/crockpot.NOTE: Searing the chicken enhances the flavor, locks in juices & gives the chicken a golden brown color. In the same skillet over medium heat (leave the drippings from the chicken in skillet as that is flavor) place in mushroom slices and minced garlic. Stir to coat.
Add in marsala and 1 cup chicken broth. Stir, scraping bottom of pan to pick up any bits from the chicken. Turn off heat. Pour mixture over chicken in crockpot.
Place lid on crockpot and cook on low for 5-6 hours or on high for 3-4 hours until temperature of chicken reaches internal temperature of 165 degrees. Remove chicken from crockpot and place on a plate. NOTE: Time will depend on size of chicken. Whisk together in a small bowl corn starch and 1/2 cup water. Pour into wine liquid in crockpot. Add in heavy whipping cream. Whisk all together. Season with additional salt & pepper, if needed.
Place chicken back into crockpot. Place lid on and cook an additional 20-30 minutes on high until sauce thickens.
Garnish with chopped parsley. I serve with cooked rice and salad. You can also serve it up with mashed potatoes or cooked pasta. Enjoy.