PREPARE dressing mix as directed on envelope, substituting lemon juice for the vinegar. Remove 1/2 cup of the prepared dressing; cover and refrigerate remaining dressing for another use.
COOK and stir chicken in 1 Tbsp. of the prepared dressing in skillet on medium heat until chicken is cooked through (170°F).
TOSS lettuce with chicken, croutons and cheese in large bowl. Add remaining 7 Tbsp. prepared dressing just before serving; mix lightly.