- 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
- Prepare grill for direct-heat cooking over hot charcoal (high heat for gas); see Grilling Procedure .
- Whisk together olive oil, sesame oil, soy sauce, vinegar, and ginger.
- Combine coriander seeds, white peppercorns, and kosher salt in a small bowl.
- Rub vegetable oil all over tuna, then coat with spice mixture, pressing gently to help it adhere.
- Oil grill rack, then grill tuna, covered only if using a gas grill, turning onto all sides, until seared on all sides but still very rare inside, 6 to 8 minutes total. Transfer tuna to a cutting board and cut across the grain into 8 slices.
- Julienne jicama using an adjustable-blade slicer fitted with 1/8-inch julienne attachment or using a knife.
- Toss watercress and jicama with enough dressing to coat, then season with salt and pepper.
- Serve tuna over salad, sprinkled with scallions. Serve remaining dressing on the side.