Heat olive oil in a skillet over medium-high heat. Cook and stir chorizo in hot oil until completely browned and broken into small pieces, 7 to 10 minutes. Remove skillet from heat; stir rice, onion, 1/4 cup taco sauce, Cheddar cheese, and cumin with the chorizo until evenly mixed.
Fill poblano pepper halves with the chorizo mixture; place in a small casserole dish or a pie pan. Drizzle 1 tablespoon taco sauce over each pepper. Pour water into bottom of the dish; cover loosely with aluminum foil.
Bake in preheated oven until peppers are tender, about 1 hour.