COOK pasta as directed on package, omitting salt.
MEANWHILE, heat 2 Tbsp. dressing in large skillet on medium-high heat. Add steak; cook 2 min. on each side or until evenly browned. Combine tomatoes, onions, mushrooms and remaining dressing; pour over steak. Bring to boil; simmer on medium-low heat 10 min. or until steak is medium doneness (160ºF).
TOP with VELVEETA; cover. Remove from heat. Let stand 2 to 3 min. or until melted. Drain pasta. Serve topped with sauce and steak.