Grilled Tuna and Watercress Salad with Asian Flavors

Name: Grilled Tuna and Watercress Salad with Asian Flavors
Ingredients: 1/3 cup extra-virgin olive oil; 1 tablespoon Asian sesame oil; 1 tablespoon soy sauce; 6 tablespoons rice vinegar (not seasoned); 2 tablespoons minced peeled ginger; 2 tablespoons coriander seeds, coarsely crushed; 2 tablespoons white peppercorns, coarsely crushed; 1 tablespoon kosher salt; 1 tablespoon vegetable oil; 1 (1-pound) sushi-grade tuna steak (about 2 inches thick); 1 pound jicama, peeled; 2 bunches watercress (10 ounces), tough stems discarded; 2 scallions, very thinly sliced