Preheat your oven to 350°F (175°C).

In a large pot, bring salted water to a rolling boil. Blanch green beans for about 4-5 minutes until bright green and tender-crisp. Transfer to ice water, then drain.

In a skillet, heat olive oil over medium heat. Sauté fresh mushrooms for 5-7 minutes until tender. If using canned mushrooms, skip this step.

In a mixing bowl, combine cream of mushroom soup, sour cream, milk, Worcestershire sauce, garlic powder, onion powder, and a pinch of salt and pepper. Whisk until smooth.

Add sautéed (or canned) mushrooms, blanched green beans, and ½ cup of fried onions to the sauce mixture. Stir gently until well-coated.

Transfer the mixture to a greased 9x13 inch baking dish, spreading evenly. Sprinkle shredded cheddar cheese on top.

Bake for 25-30 minutes until bubbling and cheese is melted.

Top with extra fried onions and return to oven for another 5-10 minutes until onions are golden brown.

Let the casserole rest for about 10 minutes before serving.