Makes 4 servings.

INGREDIENTS
1/2cup mayonnaise
3tablespoons finely chopped green onions
2teaspoons minced peeled fresh ginger
1teaspoon soy sauce
1teaspoon oriental sesame oil43/4-inch-thick tuna steaks (each about 5 ounces)
1tablespoon vegetable oil81/2-inch-thick slices crusty
country-style white bread
1/2medium english hothouse cucumber, unpeeled, thinly sliced
8radishes, thinly sliced
1ripe avocado, [...]