Separate cauliflower into small flowerets.
Cook, covered, in small amount of boiling salted water till crisp-tender, about 10 minutes; drain well.
Place hot cauliflower and beans in bowl.
In screw-top jar, combine oil, vinegar, and salad dressing mix; cover and shake well.
Pour dressing over vegetables; chill several hours or overnight, stirring occasionally.
Drain; serve vegetables on lettuce-lined plates.