Boil your quartered potatoes in a large pot of water, making sure the water covers the potatoes by at least an inch. Boil until the potatoes are soft, and easily pierced by a fork, about 15 minutes.
While your potatoes are cooking, brown the ground beef. Season with salt and pepper to taste. Once your meat is cooked, drain off excess fat. Add frozen vegetables and gravy to your ground beef skillet. Stir and simmer, until liquid is mostly combined. Only about 10 minutes.
When your potatoes are done, drain them and turn them into mashed potatoes, by mashing them with about 4 tablespoons of butter, and a couple tablespoons of milk. Mash and stir until they are just how you like them. Season with salt and pepper.
Spray a 9 x 13 casserole dish with cooking spray. First layer your meat and vegetable gravy, then cover with mashed potatoes. Spreading the potatoes can be tricky. I usually put in 6 big spoonfuls,, then use a fork to cover the first layer. Sprinkle cheese on top.
Bake, uncovered at 350 degrees Fahrenheit for 30 minutes,