Preheat your oven to 350°F (175°C).
Cook the elbow macaroni according to package instructions until al dente. Drain and set aside.
In a large mixing bowl, combine the cream of mushroom soup, milk, garlic powder, onion powder, salt, and pepper. Mix well until smooth.
Stir in the cooked macaroni, shredded cheddar cheese, and thawed green beans until everything is evenly coated.
Transfer the mixture to a greased 9x13-inch baking dish.
Sprinkle the grated Parmesan cheese evenly over the top.
Bake in the preheated oven for 25 minutes.
Remove from the oven and sprinkle the crispy fried onions on top. Return to the oven and bake for an additional 10 minutes, or until the onions are golden brown.
Let the casserole cool for a few minutes before serving.