Melt the butter in a skillet over medium high heat.
Add the onions, mushrooms, and garlic. Sauté until the onions are translucent and the mushrooms are tender (~10 minutes).
Preheat the oven to 400 degrees.
Turn the heat to medium low. Add the remaining mushroom soup ingredients and cook for 5 minutes.
Add the steamed green beans and cook until the soup reduces and is thick and creamy.
Transfer the mixture to a oven safe dish.
Top with mozzarella cheese and half the French fried onions.
Bake uncovered for 20-25 minutes.
Top with additional French fried onions before serving.