Spicy Asparagus and Lentil Salad with Fennel

Name: Spicy Asparagus and Lentil Salad with Fennel
Ingredients: 1 cup green lentils, rinsed and picked over; 1 small onion, halved; Salt and freshly ground pepper; 3/4 pound medium asparagus, tips cut to 1 inch, stems chopped; 1 medium fennel bulb—quartered, cored and thinly sliced; 1 celery rib, finely chopped; 2 small tomatoes (6 ounces each), finely chopped; 2 jalapeño or serrano chiles, seeded and minced; 2 tablespoons coarsely chopped cilantro; 2 tablespoons coarsely chopped flat-leaf parsley; 3 tablespoons fresh lemon juice; 1 1/2 tablespoons extra-virgin olive oil; 1 1/2 tablespoons soy sauce; 1 medium Belgian endive, spears separated; 4 cups loosely packed mixed baby lettuces (3 ounces)