In a large pot, boil the rice in salted water until tender. Drain and set aside.
Cut tops off the peppers and remove the seeds. Save the tops.
In a large pot, parboil the peppers for 5 minutes to soften them. With tongs, remove the peppers and set aside. (You can soften the peppers in the microwave instead of parboiling them. Just put them upside down on a plate, cover, and microwave them for three to four minutes.
In a large skillet over medium heat, sauté the ground beef and onions, finely chopping the ground beef with a chopping tool and cooking it until the beef is browned.
Drain the grease.
Add the cooked rice, ketchup, salt and pepper to the ground beef and onions.
Stuff each pepper with the filling and place the peppers in a casserole dish. Add the top of the pepper with the stem if you wish.
Pour about 1/3 cup of water in the bottom of the casserole dish.
Cover with foil and bake at 350° for about 20 minutes until the peppers are tender.
Serve with additional heated ketchup.