Bring a small pot of salted water to a boil. Cook the macaroni to al dente according to the package instructions. Drain and hold until the meat mixture is ready.
In a cast-iron pan, heat the oil over medium heat. Add the onions and sweat until translucent, 5 to 8 minutes. Add the garlic and cook for another 1 minute. Add the ground beef, season with salt and pepper and cook until starting to brown, 3 to 5 minutes. Add the tomatoes and cook for another 2 to 3 minutes. Add the cream and cook until the mixture is reduced, about 10 minutes. Turn off the heat, add the cheese and stir until well incorporated. Stir in the cooked macaroni and season with salt and pepper.
Cut each pepper around the stem and remove to create a lid. Remove the seeds and, if the peppers do not sit flat, trim the bottoms slightly; just be careful not to cut a hole in the bottom of the peppers. Using the tip of a small serrated knife, cut a face like a jack-o'-lantern into the side of each pepper.
Fill the peppers with the beef mixture and put on a baking sheet with the lids on the side. Bake until the peppers are fork-tender, about 30 minutes.