First, drain and rinse the green beans. Preheat the oven to 350℉
Now, wash and chop the mushrooms. Add them into a sauté pan and cook the mushrooms until the water has evaporated and they are withered down. This is crucial to do before making the recipe. If you do not all that excess water will end up inside the casserole.
Add them into a large bowl or the casserole dish. Then, add in the cream of mushroom, Worcestershire sauce, mushrooms, half the shredded cheese then season with salt and pepper to taste. Add the other half of the shredded cheese across the top.
Place in the preheated oven for 20 minutes. Then, add the crispy onions and cook another 10 minutes or until golden brown.
Allow the cheesy green bean casserole to cool a bit before serving.