Using a sharp knife, butterfly the chicken breast by carefully slicing lengthwise into cutlets
Cover with plastic wrap and pound to an even thickness
Season the chicken cutlets on both sides garlic powder, dried parsley, freshly cracked black pepper and salt
Heat a large sauté pan over medium high heat and spray with avocado oil
Sear the chicken on each side for 1 minute; reduce heat to medium and cook for 4-5 minutes then remove from the pan and set aside
Reduce heat to medium low, spray with a little more avocado oil and add the butter
Add the onions and mushrooms and season with a pinch of salt
Cook for 8-10 minutes or until softened and the liquid from the mushrooms has mostly evaporated
Add the garlic, sprinkle in the flour then mix and toast for 2-3 minutes
Add the milk, cream and Dijon mustard then stir until combined
Bring to a simmer and cook for 10-12 minutes until thickened then season with salt and pepper to taste
Return the chicken to the pan and cook for 5-6 minutes or until cooked through
Serve with mashed potatoes, rice or roasted vegetables and top with fresh parsley