COMBINE VELVEETA, 1/2 cup tomatoes and milk in microwaveable bowl. Microwave on HIGH 2 to 4 min. or until VELVEETA is completely melted, stirring after each minute. Mix reduced-fat cream cheese, chicken and onions.
BRUSH tortillas with oil. Stack 4 tortillas on microwaveable plate. Microwave 30 sec. or just until softened; set aside. Repeat with remaining tortillas.
SPOON about 1/4 cup chicken mixture down center of each tortilla; roll up. Place, seam-sides down, in 12x8-inch microwaveable dish. Top with VELVEETA sauce and remaining tomatoes. Microwave 10 min. or until heated through, turning dish every 3 min.