Preheat oven to 350 degrees F
In a large bowl place green beans and soup. Mix well and heat in the microwave for 3 to 5 minutes on HIGH until warm or you can boil it on simmer for 10 minutes. Stir in 1/2 cup of cheese and heat for another 2 to 3 minutes.
Transfer green bean mixture to a casserole/baking dish and sprinkle with remaining cheese and onions.
Bake in a preheated 350 degrees F oven until the onions just begin to brown and the cheese melts.