Start by preheating your oven to 350°F so it’s hot and ready. In a bowl, combine the condensed mushroom soup, milk, softened cream cheese, and garlic. Stir until the mixture becomes smooth and creamy, using a whisk if the cheese needs more help blending.
Next, drain your green beans and gently fold them into the creamy mixture. Stir in about two-thirds of your fried onions so they’re mixed throughout. This gives the casserole body and flavor from the inside.
Transfer everything into an oven-safe baking dish and pop it in the oven for around 30 minutes. If the top starts browning too much, you can loosely cover it with foil.
After baking, take it out and sprinkle the remaining crispy onions, grated cheese, and optional walnuts on top. Return to the oven for about 5 minutes so the topping turns golden and melty.
Once out of the oven, finish by scattering scallions over the top. Add parsley or extra cheese if you want and serve while hot!