1 (10.75 ounce) can condensed cream of mushroom soup
1 (6 ounce) can French fried onions
1 cup shredded Cheddar cheese
Preheat oven to 350 degrees F (175 degrees C).
Place green beans and soup in a large microwave-safe bowl. Mix well and heat in the microwave on HIGH until warm (3 to 5 minutes). Stir in 1/2 cup of cheese and heat mixture for another 2 to 3 minutes. Transfer green bean mixture to a casserole dish and sprinkle with French fried onions and remaining cheese.
Bake in a preheated 350 degrees F (175 degrees C) oven until the cheese melts and the onions just begin to brown.