Preheat the oven to 350 degrees F (175 degrees C).
Mix green beans and condensed soup together in a large microwave-safe bowl until well combined. Microwave on high until warm, 3 to 5 minutes.
Stir ½ cup Cheddar cheese into the green bean mixture. Microwave on high for 2 to 3 minutes.
Transfer mixture to a casserole dish and spread evenly over the bottom. Sprinkle remaining Cheddar over top, then sprinkle with the French-fried onions.
Bake in the preheated oven until cheese is melted and the onions are just turning brown, about 10 minutes.
