In a bowl, stir together flour, garlic powder, sea salt, and pepper. Pour onto a plate or large bowl.
Dredge both sides of the chicken through the flour mixture making sure it is well coated.
Add the avocado oil and optional butter alternative to skillet. Turn heat to medium-high.
Place the chicken breasts in the skillet and cook for 3 minutes on each side or until a golden brown.
Remove chicken from skillet to a plate and set aside.
Add additional avocado oil (and optional butter alternative) if needed and place on medium heat.
Add garlic and mushrooms to skillet and stir until golden - roughly 3 minutes.
Add 1/2 cup of chicken broth to skillet to deglaze skillet and cook for additional 2 minutes.
Add remaining broth, Marsala wine, and coconut milk to the skillet and bring to boil. Allow the sauce to boil until it starts to thicken and reduce. May add optional cornstarch if needed.
Place chicken back in the skillet and cover the skillet. Cover and cook for 10 minutes. Then flip chicken and cook for additional 3 minutes till chicken is done.