Heat oil in skillet over medium heat.
Add onions and garlic and cook two minutes, stirring occasionally. Add sliced mushrooms and cook 1 minute longer. Cut chicken into thin strips; add to the skillet and cook, stirring, until browned on all sides.
Stir in soup, milk, and pepper; bring to a boil. Add rice; reduce heat to low. Cover and cook until rice is done, stirring occasionally.
Garnish with additional chopped green onions, if desired.
Serves 4 to 6.