Cut the beets into quarters or sixths. Whisk together the lemon zest and juice, onion, herbs, coriander, 1/4 teaspoon salt, pepper to taste, and the oil in a small bowl. Taste the dressing on a beet and correct the seasonings if needed. Toss the beets with enough dressing to coat lightly. Toss the greens with the remaining dressing and arrange them on salad plates. Add the beets and olives (if using) and serve.
Serves 4 to 6