In large skillet, melt margarine over medium-high heat. Add chicken; cook and stir 5-6 min. or until browned.

Slowly add water and milk; bring to a boil. Slowly stir in pasta and seasoning mix. Separate pasta with fork. Return to a boil.

Reduce heat to medium. Boil uncovered, 4-5 min. or until just tender, stirring frequently. Stir in tomatoes, if desired.

Sauce will be thin. Let stand 3-5 min. to thicken.