Fry the onions, chilies, and add the garlic after about 5 minutes. Add the chicken pieces. Cook on a low heat until the chicken pieces are cooked through - about 10 minutes. Meanwhile mix the yogurt, sour cream and mushroom soup in a large bowl. Add contents of the frying pan and stir in seasoning. Fill the burritos with the mixture and roll them up, putting them seam-side down in a dish or baking tin. Pour over the rest of the filling, sprinkle with the grated cheese and put in a hot oven (400°F) for 15 minutes, or until the cheese is toasted. Serve with a green salad or rice.