In a small bowl or container combine the rice vinegar, olive oil, shallots, mustard, and salt and pepper. Stir or shake to combine.
In a large bowl combine the lettuce, celery, onion, bell pepper, then add the dressing and toss to combine. Transfer to a serving bowl, and sprinkle over the queso fresco.
Notes
Vidalia is a nice onion to use in salads when you are introducing onions to kids or to people who think they don’t like onions (many people just get nervous that onions will be too strong—they add so much flavor to dishes, both raw and cooked, that they are a shame to miss out on. Use Vidalias, or other sweet onions, as a gateway onion.