Preheat the oven to 425 degrees F. Oil a 3 or 4 cup ovenproof baking dish.
In a dry medium skillet, saute the chorizo over medium-high heat until almost crisp. Remove the chorizo to a plate. Add the onions and garlic to the pan juices and cook until soft, about 5 minutes. Return the chorizo to the skillet with the onions and garlic and stir to combine.
Put half of the cheese in the baking dish and sprinkle with half of the chorizo mixture. Repeat with the remaining cheese and chorizo mixture. Bake until the cheese is bubbling, about 20 minutes. Serve with flour tortillas for soft tacos.