Preheat your oven to 350°F (175°C).
In a large pot, boil the sliced potatoes until just tender, about 10 minutes. Add the green beans and cook for an additional 5 minutes.
Drain the vegetables and set aside.
In a mixing bowl, combine the cream of mushroom soup, milk, garlic powder, onion powder, salt, and pepper.
In a large baking dish, layer the potatoes and green beans, then pour the soup mixture over the top.
Sprinkle the shredded cheddar cheese on top of the casserole.
Bake in the preheated oven for 25-30 minutes, or until the cheese is bubbly and golden.
Remove from the oven and top with crispy fried onions. Return to the oven for an additional 5 minutes.
Let cool slightly before serving.