Prepare hamachi by ensuring that the fish is completely defrosted in the refrigerator (if frozen). Gently dry between two paper towels. Transfer to a sheet pan and set aside.
Add sesame seeds to a small pan and heat over medium-high heat. Toast for about 5 minutes, or until white sesame seeds, are lightly golden in color and fragrant. Move them around every minute to get even toasting with no burning. Transfer to a small bowl.
Lightly brush the hamachi with grapeseed oil on each side. Lightly season each side with salt and pepper.
Generously sprinkle the toasted sesame seeds on all 4 sides of the fish, until the surface is completely covered. Lightly press the seeds onto the surface. Lightly cover with plastic wrap and transfer to the refrigerator while you make the salad.
Soba Noodle Salad
Cook soba noodles according to package directions. Drain noodles and rinse with cool water until no longer hot, and then allow the water to drain again. Transfer to a large bowl.
In a medium-sized bowl whisk together soy sauce, rice vinegar, sesame oil, and honey.
Assembly
In a large bowl toss together cooled noodles and dressing. Portion noodles into serving bowls and top with edamame beans, cucumber, carrots, bell pepper, red cabbage, and peas.
Take the sesame-crusted hamachi out of the refrigerator. Carefully transfer it to a clean cutting board. Using a sharp chef's knife, slice about ¼-inch wide pieces against the grain (try to use only 1 to 2 cutting motions). Add even portions of the fish to each bowl, laying in a fan shape. Serve with additional soy sauce and lime wedges if desired.