I've used this recipe for 35 plus years. It came from a young girl I knew many years ago. She brought this dish to a pot luck, and shared her recipe in our company cookbook. My copy of the cookbook is worn and tattered , but TREASURED beyond measure :) This recipe is tried and true many times over !! I have made it in the oven, and it also works beautifully in the crock pot (just cook on high about 4 hours and it comes out perfect !!). The filling is so fluffy and tender, NOT a hard, dry, meatball, like so many recipes turn out to be. This is THE ONLY recipe I use for stuffed greeen peppers :)
Brown the ground beef and onion together in a large fry pan. Add the rice-a-roni (and the included seasoning packet),the 14.5 ounce can diced tomatoes (undrained), and 2 cups of water. Bring to a boil, reduce heat, cover and let simmer for 20-30 minutes until rice is done. Cool slightly.
***(It is best to use the meat/rice mix while it's hot because it helps to cook the peppers)
Combine the brown sugar, 2 cans tomato sauce, cider vinegar, and dry mustard. Pour into the bottom of your baking dish.
Remove tops and seeds from washed peppers. Fill peppers with the hot meat/rice mixture and place in baking dish. If you have any meat/rice filling left after you fill your peppers just spoon it in between the peppers in the baking dish.
Cover the baking dish with a lid or seal it well with foil. Bake at 350 degrees for an hour. Remove lid and sprinkle with a little grated cheddar cheese if you like. Serve and enjoy a great comfort food !!