For the salad: Layer the salad ingredients in a large salad bowl, beginning with the lettuce, then adding the tomatoes, bell pepper and onion.
For the French dressing: Put the vinegar, sugar, mustard, onion, paprika, salt and 1/2 cup water in a blender and process until well blended. While the blender is running, slowly stream in the oil. Chill in the refrigerator for 3 hours.
When ready to serve, pour some of the dressing over the salad and toss.