In a large skillet brown ground beef. About 1/2 way through cooking the beef add in 1/2 a package of onion soup mix, and let it cook the rest of the way with the beef. Taste this before adding any additional salt, as the onion soup mix can be quite salty on it's own! Drain the beef completely and pat it dry to soak up any additional grease left behind.
While the beef is cooking, prepare your potatoes per the package directions....I usually add in sour cream, butter, and chopped bacon to the potatoes for extra flavor. In a deep oven safe dish or a 9x13 baking dish spread a layer of potatoes in the bottom. Layer the remaining ingredients as follows....Beef mixture...Green Beans...Tomato soup and french's cheddar onions if you're using them. ...and the last part of the mashed potatoes.
Place casserole in the oven for 20-30 minutes, or until heated through and the potatoes begin to get a golden color.
At the last 5 minutes sprinkle cheese over top of the dish and cook until melted completely. This is an all-in-one dish, and can be served with a light salad on the side.