Prepare your bell peppers. You need to decide if you want to slice the peppers in half (half peppers lie flat in pan; you will need more pan space) or just remove the top and seeds (peppers stand upright in the pan; you won't need as much pan space). See photos. I like to slice the peppers in half because this means you get more crispy cheese on top of each serving. Remove the seeds and membranes from each pepper. If you are slicing the peppers in half, leave the stem on so that the filling doesn't spill out from the top.
Pre-cook your peppers. I love to do this in the microwave because it is SO easy. Place the peppers cut-side-up in a microwave safe dish, like a glass 9x13 inch pan. Add 1/2 cup water to the bottom of the pan. The peppers should not be stacked. Sprinkle with 1 teaspoon kosher salt. Microwave for 5 minutes on high. Discard the water in the bottom of the pan. (You might have to do this in a couple batches if you halved your peppers. 6 whole peppers sitting upright will fit in a 9x13 or even a 2-quart pan, but 12 pepper halves won't. Microwave them in another dish, and then transfer the cooked peppers to a large rimmed baking sheet.) If you don't have a microwave, you can also boil or bake the peppers to precook them. See notes.
Cook your rice. If you don't have leftover rice (you need 1 to 1 and 1/2 cups cooked rice), cook some now. In a small saucepan, add 3/4 cup dry white rice and 1 cup + 2 tablespoons water. Add 1/2 teaspoon kosher salt. Turn the heat to high and bring to a boil with the lid on. Once it boils, turn the heat down to low and continue cooking another 10 minutes (lid on). Turn the heat off and leave the lid on for another 5 minutes. Fluff with a fork.
Prepare the filling. In a 12 inch skillet, cook 1 pound ground beef and 1 chopped onion over medium high heat for 5-10 minutes until the ground beef is cooked and no longer pink, and the onion is soft. Drain the grease from the pan.
Add 3 cloves of smashed and minced garlic to the pan over medium high heat and cook for 1 minute until fragrant.
Add 2 tablespoons Worcestershire sauce and 1/4 teaspoon liquid smoke.
Add 2 teaspoons Italian seasoning, 1 and 1/4 teaspoons kosher salt, 1/2 teaspoon black pepper, 1/2 teaspoon garlic powder, 1/2 teaspoon smoked paprika, and 1/4 teaspoon crushed red pepper.
Add a 15 ounce can of diced tomatoes. Let cook for a while over medium high heat, about 3 minutes. Remove from heat.
Add 1 cup frozen corn and the cooked rice (you don't have to add all the rice if you don't want to.) Mix it all together. Adjust seasonings to taste.
Spoon the filling into each pepper. Top each stuffed pepper with about a tablespoon of mozzarella cheese, or any kind of cheese you like.
Bake at 350 for about 20-25 minutes, until the cheese is melted. You should be able to easily slide a fork into the side of a pepper. If it seems to hard, let it bake a few more minutes.
Let cool a few minutes and enjoy!