The Tuna Burger

Ingredients

• 2 pounds yellowfin tuna fillets, chopped fine by hand, removing any sinew
• 3 tablespoons finely chopped scallion
• 2 tablespoons freshly grated gingerroot
• 2 teaspoons Dijon-style mustard
• 1 tablespoon soy sauce
• Cayenne, to taste
• Salt and freshly ground pepper
• Vegetable oil
• 1/2 cup bottled mayonnaise
• 1 tablespoon wasabi powder mixed with water to make a paste
• 1 tablespoon fresh lime juice
• 1 seedless cucumber, peeled, cut in half and very thinly sliced
• 1 small red onion, very thinly sliced
• 2 tablespoons finely chopped pickled ginger, available in Asian specialty stores and gourmet food shops or 2 tablespoons grated fresh gingerroot
• 1/4 cup seasoned rice vinegar, available in most major supermarkets or 1/4 cup white wine vinegar plus 1 tablespoon sugar
• 4 brioche rolls or other soft roll