How to Make It
In a small saucepan, combine the chicken stock, soy sauce, honey and mirin and bring to a boil. Simmer over moderate heat, stirring occasionally, until reduced to a glaze, about 12 minutes. Let the glaze cool slightly.
Set up an ice bath. In a large saucepan of salted boiling water, blanch the green beans until crisp-tender, 2 to 3 minutes. Using a slotted spoon, transfer to the ice bath to cool. Drain the greens beans well and pat them dry.
In the saucepan of salted boiling water, cook the soba until al dente, 3 to 4 minutes. Drain and cool under cold running water, then pat dry with paper towels. In a large bowl, toss the soba with the lime juice, sesame oil and 3 tablespoons of the glaze. Fold in the green beans, radishes, romaine, the 1/2 cup of basil and the sliced scallion and season with salt and pepper.
Season the arctic char with salt and pepper. In a large nonstick skillet, heat the grapeseed oil until shimmering. Add the fish, skin side down, and press gently with a spatula to flatten. Cook over moderately high heat until the skin is browned and crisp, about 4 minutes. Flip the fish and cook until medium within, about 1 minute longer. Transfer to plates. Spoon the soba salad alongside, garnish with basil and serve, passing the glaze at the table.