Whisk orange juice, shallots, vinegar, lemon juice and orange peel in small bowl. Gradually whisk in oil. Season with salt and pepper. Dressing can be made 24 hours ahead. Cover; chill. Bring to room temperature and whisk again before serving.
Place onion in large bowl. Add 1/3 of dressing; toss. Let marinate 20 minutes.
Add arugula, mint, and olives to onions and toss. Add additional dressing to taste. Add additional salt and pepper, if necessary. Divide salad among 6 plates. Top with orange slices and ricotta salata slices.