Preheat and Prepare
Preheat your oven to 375°F (190°C).
Bring a large pot of salted water to a boil. Add the green beans and potatoes and cook for about 5 minutes until just tender. Drain and set aside.
Make the Sauce
In a mixing bowl, whisk together the cream of mushroom soup, milk, garlic powder, onion powder, salt, and pepper.
Assemble the Casserole
In a 9x13-inch casserole dish, layer the cooked green beans and potatoes. Pour the soup mixture over the top and stir gently to coat.
Sprinkle the shredded cheddar cheese evenly over the mixture.
Bake
Bake uncovered for 25-30 minutes, or until the sauce is bubbly and the cheese is melted.
Add the Topping
Remove the casserole from the oven and sprinkle the crispy fried onions over the top. Return to the oven and bake for an additional 5-7 minutes until the onions are golden brown.
Serve
Let the casserole cool for a few minutes before serving warm.