Rinse and trim the scallion. Coarsely dice the white and light green parts. Thinly slice and reserve the green parts for garnish. Peel the cucumber. Blanch the tomatoes in boiling water briefly. Remove from the water and peel. Quarter the tomatoes and remove the core. Coarsely chop the tomatoes and the cucumber. Puree the coarsely chopped vegetables with the remaining ingredients in the blender. Season the mixture to taste with salt and pepper.
Fill 2 glasses half-full with crushed ice. Top with the vegetable juice, garnish with the scallion greens, and serve.