Season both sides of chicken breasts with thyme, oregano, salt and pepper.
Heat 1 tablespoon olive oil in a large skillet over medium heat. Add the chicken in a single layer. Cook on the first side for 3 to 4 minutes, until brown, flip and brown on the other side, about 2 additional minutes. The chicken does not need to be cooked all the way through. Note: If using the Crock-Pot Express Cooker, use the sauté function for this step to brown the chicken on both sides.
Transfer the chicken to the pot of a slow cooker.
Top with mushrooms and garlic.
Pour the marsala cooking wine over the ingredients.
Cover with the lid and cook on LOW for 4 to 5 hours or HIGH for 2 to 3 hours. Chicken is done when internal temperature reaches 165 degrees Fahrenheit.
Remove the chicken from the slow cooker and transfer to a plate.
Whisk together the cornstarch and water in a small bowl and add to the slow cooker. Pour in the heavy cream. Cook on HIGH for 15 minutes, or until thickened.
Return the chicken to the slow cooker and let heat for5 minutes to warm through.
Serve with pasta, rice, bread or potatoes. Garnish with parsley and enjoy!