1. Prepare Sweet Onion Vinaigrette and Toasted Bun Croutons.
2. Toss together watercress, next 5 ingredients, and 1/4 cup vinaigrette in a large bowl. Arrange mixture on a serving platter. Sprinkle with queso fresco, and top with jalapeño pepper slices and croutons. Serve salad with remaining vinaigrette.
Total time includes vinaigrette and croutons.