PREPARE Dinners in large saucepan as directed on package. Meanwhile, heat dressing in large skillet. Add chicken and half the onions; cook 5 to 8 min. or until chicken is done, stirring frequently.
HEAT oven to 350ºF. Spoon Dinners into 13x9-inch baking dish sprayed with cooking spray. Top with chicken mixture. Blend tomatoes and jalapeño pepper in blender until smooth; spread over chicken mixture. Top with cheddar; cover with foil.
BAKE 30 min. or until casserole is heated through, removing foil after 25 min. Top with cilantro and remaining onions.