In a small bowl, combine the oil, vinegar, and salt. Marinate the roasted peppers and onions in the vinaigrette for 15 minutes.
To plate the salad, arrange the peppers (reserve the vinaigrette), mozzarella, and arugula as desired. Drizzle the reserved vinaigrette over the arugula and serve.
- A country bread crouton flavored with fresh herbs would serve as a great accompaniment in this salad.