Preheat oven to 350. Prepare a 9" x 13" pan with cooking spray; set aside. In a saucepan cook, chicken and onions until chicken is no longer pink. Stir in dressing mix, sour cream, and half the picante sauce. Mix well and bring to a boil through. Spoon 1/2 cup of the chicken mixture onto each tortilla. Fold one edge of each tortilla over the filling; this keeps the filling from spilling out. Roll up burritos and place seam-side-down in the prepared pan. Spread the remaining picante sauce evenly over top burritos and sprinkle cheese evenly over top. Bake for 20 minutes or until heated through.