2 tablespoons wasabi powder (horseradish powder)*
1 1/2 tablespoons water
1/2 cup mayonnaise
1 pound fresh tuna steaks, cut into 3/4-inch cubes
2 1/2 tablespoons soy sauce
28 large slices pickled ginger*
28 8-inch wooden skewers
1 bunch watercress
1 teaspoon freshly ground black pepper
1 tablespoon vegetable oil
Mix 2 tablespoons wasabi powder and 1 1/2 tablespoons water in small bowl to blend. Whisk in 1/2 cup mayonnaise.
Cover wasabi mayonnaise and refrigerate at least 30 minutes. (Can be made 1 day ahead. Keep refrigerated.)
Combine tuna and soy sauce in medium bowl; toss to coat.
Marinate tuna 30 minutes at room temperature, stirring occasionally.
Meanwhile, thread 1 ginger slice onto each skewer 2 inches from tip.
Line platter with watercress. Place bowl of wasabi mayonnaise on platter.
Drain tuna; pat dry. Return to medium bowl. Sprinkle with pepper; toss to coat.
Heat oil in large skillet over medium-high heat.
Add tuna and sear until browned on all sides but still pink inside, about 2 minutes total.
Thread 1 tuna cube onto each prepared skewer next to ginger.
Arrange skewers on platter and serve.
*Available at Japanese markets and specialty foods stores and in the Asian foods section of some supermarkets.
Makes 28.