Preheat the oven to 325 degrees F (165 degrees C).

Heat condensed soup in a saucepan over medium heat. Stir in processed cheese and bacon bits; continue stirring until completely melted. Remove from heat; stir in mushrooms and green beans until evenly coated.

Pour mixture into a casserole dish; top with fried onions, leaving a 1-inch border along the sides.

Bake in the preheated oven until heated through and bubbly, 25 to 30 minutes. Check near the end of cooking to ensure onions aren't getting too brown.