Add the two cans of undiluted cream of mushroom soup to a medium sized bowl.

Add in the milk, shredded cheese (if using), and ground black pepper. Fold together using a silicone spatula until thoroughly combined.

Add 2lbs of frozen French style green beans to the insert of a 6 quart slow cooker.

Pour the soup mixture on top of the green beans, and stir as well as you possibly can to distribute the soup mixture over the beans. Since they are frozen, this will be difficult to do, but will get easier once the beans have thawed.

Place the lid on the slow cooker and cook on high for 3 ½ to 4 hours, stirring several times to help distribute the soup mixture on top of the green beans and to help thaw any remaining frozen beans.

Once the casserole is bubbly, hot and cooked through, prepare your french fried onions. You want them to be crispy, so I have three methods for ensuring a crispy French fried onion.

Method 1: Add 1 tablespoon of butter to a medium sized skillet over medium heat. Once melted, add the French fried onions and toss with the butter. Stir frequently, toasting the French fried onions in the skillet. Once they have changed to a more golden hue, spread on top of the casserole and serve immediately.
Method 2: Add the French fried onions to an air fryer and cook at 350F for 1-2 minutes. (This is my favorite method!)
Method 3: Add the French fried onions to a broiler safe pan and place under broil for about 1 minute, watching them carefully to avoid burning.
Alternative: If you would prefer, you can place the French fried onions on top without toasting them or crisping them up, but the results will not be as crunchy!

Serve immediately and enjoy!