If using the fresh mushrooms: melt the butter in a skillet, over medium heat. Sautee mushrooms and garlic until tender. Drain. And put to the side.
If using canned mushrooms: drain and mix with garlic.
Heat oil up in the same skillet, on med heat. Dredge chicken in flour and cook in the oil. When chicken is mostly cooked, add the mushroom and garlic mix and the ranch dressing. warm until chicken is throughly cooked and the sauce is warm. Garnish with green onions