Add 1 in. of water to a saucepan; add cauliflower. Bring to a boil. Reduce heat; cover and simmer for 5-8 minutes or until crisp-tender. rinse in cold water; drain and place in a large bowl. Add zucchini, onions and olives; toss.
In a jar with a tight-fitting lid, combine the oil, orange juice, vinegar, tarragon, orange peel, salt and pepper; shake well.
Pour over cauliflower mixture and toss to coat. Cover and refrigerate for 2 hours. Just before serving, toss with salad greens.