Cook your choice of rice according to the package instructions. Set aside 2 cups for the filling. This step can be done in advance.
Dice the onions, bell pepper, and tomatoes.
(Optional: reserve a few bright tomato pieces to scatter on top of the stuffed peppers for color.)
In a large skillet or pot, brown the chorizo over medium to medium-high heat. Drain most of the grease, leaving about 2 tablespoons in the pan.
Add the diced onion and bell pepper. Sauté until just translucent, about 3–5 minutes.
Stir in taco seasoning, oregano, garlic, salt, and pepper to coat the mixture. Let the seasonings bloom for about 30 seconds.
Add the diced tomatoes and stir well, scraping up any browned bits from the bottom of the pan.
Mix in the cooked rice and first cup of shredded cheese. Stir to combine.
Taste and adjust seasoning if needed.