Cut the tops of the peppers off and set aside; core and seed the insides. In a pan deep enough to submerge the peppers, bring enough water to boil to submerge the peppers. Once the water boils, add the peppers, submerging them so they don't float. Cook until almost tender; depending on the thickness of the pepper, this will take 5 to 10 minutes. Remove the peppers from the pan, draining the water from inside them, and set aside.
Meanwhile, cook the rice according to instructions. Generally, the rice-to-water ratio is 1 part rice to 2 parts water. Adding salt and a fat (butter or olive oil) is optional, but for this recipe it's not recommended. Set aside.
At the same time, in a large skillet, brown the ground beef and drain most of the fat, retaining only a very small amount (a couple tablespoons or so).
Add the chopped onion and minced garlic to the beef and cook until the onion is translucent. This is why you retain a little of the beef fat.
Mix the tomato paste with the water. Add the tomato paste mixture along with the can of diced tomatoes to the beef mixture. Simmer until only about ½ cup of liquid remains, about 15 minutes.
Now add the rice to the beef and tomato mixture. Add salt and pepper and mix thoroughly so the rice is coated with the tomato mixture. Taste it for any needed salt and pepper and add more if needed to suit your taste.
Prepare an 8"x8" baking dish with cooking spray oil or other fat to prevent the rice from sticking. Add some rice to the bottom of the dish to help prop the peppers in place. Place the peppers in the dish upright and spoon and lightly pack the rice and beef mixture into the peppers. Use the remaining rice mixture to create a nest around the peppers and place the tops back onto the peppers.
Bake uncovered on a middle rack for 3 minutes at 350°. Cool for about 5 minutes, serve and enjoy!