Preheat oven to 350 degrees.
Melt butter in a skillet.
Add diced onions to the butter and sauté until translucent.
Add in the bacon bits and garlic and sauté until warm and fragrant.
Stir in the can of cream of mushroom soup, pepper, drained green beans and cheese.
Once the cheese is melted, sauce is bubbling and green beans are warm, stir in 1/4 to 1/3 of your french fried onions into the mixture.
Now taste test for salt. The cheese, cream of mushroom, bacon and french fried onions are all salty and it is very likely you will not even need salt at all. Also remember, the remaining french fried onions will be put onto the top of the casserole mid baking which will add additional saltiness.
Transfer your casserole mixture to a 9x13 greased baking dish and smooth into one even layer.
Bake in the oven for 20 minutes or until bubbly.
Remove from the oven and top with the remaining french fried onions.
Bake in the oven for an additional 10-15 minutes.
Remove from the oven, serve and enjoy!