In a medium bowl, combine avocado, vinegar, ginger and salt. Mash with fork. Stir in cilantro. Cover tightly by pressing plastic wrap directly on to the surface of the aioli to prevent discoloration. Set aside while grilling salmon.
Brush salmon or halibut fillets with 2 tablespoons of the olive oil. Grill or broil for 3 to 4 minutes per side, turning once.
Brush remaining olive oil on bread slices and grill or toast.
Arrange half cup arugula on each toast slice. Top with salmon fillet and one quarter of the avocado aioli. Drizzle with hoisin sauce and sprinkle with toasted sesame seed.