Preheat oven to 350.
Wash and dry the peppers and cut them in half lengthwise. Discard the stems and seeds and scrape out the veins. Lay pepper halves in a large baking dish.
Squeeze the chorizo out of its casing into a medium bowl. Add rice, cilantro, onion, garlic, fajita seasoning, and 1/2 cup cheese and thoroughly mix (optional: use 1/2 cup goat cheese instead of cheddar). Spoon stuffing into each pepper half, being sure to pack it down.
Bake peppers for 30 minutes. Remove from oven and top peppers with the remaining 1 cup grated cheese. Return to oven and back 15 minutes more, until stuffing is cooked through and cheese is melted into it.