Chop cauliflower into rice-like shapes using a vegetable chopper and set aside.
Mix diced tomatoes, tomato sauce, garlic salt, and Italian seasoning together in a bowl and set aside.
Bring a large pot of water to a boil. Add bell peppers and cook 5 to 7 minutes. Remove from water and set aside to cool.
Preheat the oven to 400 degrees F (200 degrees C).
Heat a large skillet over medium heat. Cook and stir hamburger meat in the hot skillet until browned and crumbly, 5 to 7 minutes. Drain and discard grease. Clear an area in the center of the skillet and add chorizo. Cook about 5 minutes; stir into hamburger meat in the skillet. Add chopped cauliflower and cook, stirring frequently, about 10 minutes.
Remove skillet from heat and add 1/2 the tomato sauce mixture. Stir thoroughly.
Fill each bell pepper with meat mixture and place in a small glass casserole dish. Cover with remaining tomato sauce mixture.
Bake in the preheated oven for 20 minutes. Remove stuffed peppers from the oven and cover with shredded Cheddar cheese. Return to the hot oven and bake until cheese is melted, about 5 minutes more.