Preheat the oven to 350°F. Grease a 9-by-13-inch baking dish with cooking spray.
Spread an even layer of sliced potatoes over the bottom of the dish. Season with plenty of salt and pepper on top. Top the potato layer with the browned ground beef.
Top the ground beef layer with a layer of sliced onions and season generously with salt and pepper.
Top the onion layer with an even layer of diced tomatoes and season generously with salt and pepper.
Top the tomato layer with the chopped green bell peppers.
Cover the baking dish with aluminum foil. Bake this Dolly Parton casserole, covered, for two hours. Then remove the dish from the oven, uncover, and allow it to cool slightly before serving.
