Cut baguette into slices and toast lightly. Add the oyster sauce, mirin, rice vinegar, and sesame oil in a small bowl and mix sauce well, then set aside.
Dice salmon and tuna.
Mix the diced salmon and tuna with green onion and sesame, then stir in the sauce.
Place tomato, avocado, and cucumber slices on toasted baguette. Add fish mixture and imitation crab on top.
Drizzle each with the sauce and Sriracha mayo. Finally, top with masago and serve!