How to Make It
In a skillet, bring the wine, fish stock and shallot to a boil. Add the scallops in a single layer and simmer over moderate heat, turning once, until cooked through, about 5 minutes. Transfer the scallops to a plate and keep warm.
Bring 1/2 cup of the poaching liquid to a boil in a saucepan. Whisk in the dissolved arrowroot and cook over moderate heat until slightly thickened. Remove from the heat, whisk in the oil and vinegar and season with salt and pepper.
In a large pot of boiling salted water, cook the green beans just until tender, about 6 minutes. Drain.
Spread the beans on 4 plates. Thickly slice the scallops and set them on the beans. Drizzle with the vinaigrette, garnish with the tomato and tarragon and serve.