TOSS cactus, onion, tomato, cilantro and lime juice in medium bowl. Season to taste. Add cheese; mix lightly.
ADD a pinch of salt to vinegar in small bowl; stir until salt is dissolved. Gradually add oil, stirring with wire whisk until well blended.
DRIZZLE just enough dressing over the salad to moisten all ingredients; toss lightly, Serve any remaining dressing on the side.
