Tuna Tartare with Avocado

• 1 pound (450 g) sashimi-quality tuna
• 2 tablespoons Dijon mustard
• 2 tablespoons extra virgin olive oil
• 2 tablespoons low-sodium soy sauce
• 2 tablespoons rice vinegar
• 1 teaspoon vegetable powder dissolved in 1/4 cup (60 ml) water
• Kosher salt
• Freshly ground black pepper
• 1 firm ripe avocado
• Snipped chives, for garnish

Cut the tuna into 1/4-inch-Wide (6 mm) strips, then into 1/4-inch (6 mm) cubes. Transfer to a bowl, cover, and refrigerate. Place the mustard, oil, soy sauce, vinegar, dissolved vegetable powder, salt, and pepper in a blender and combine. Refrigerate. Before serving, peel the avocado and cut it into  (13 mm) cubes. Using a fork, gently combine it with the tuna. Season to taste. TO SERVE: Place equal amounts of sauce on four appetizer plates. Pack the tuna-avocado mixture tightly into a 1/2-cup (125 ml) measure and invert it onto the sauce. Garnish with chives.