Make the dip: Puree the dressing, cucumber, horseradish, milk, vinegar, wasabi powder, cayenne pepper, and salt to taste in blender untill smooth. Cover and refridgerate until ready to serve.
Prepare the beans: Fill large bowl with ice water. Bring the broth to a boilin a saucepan over high heat. Add the green beans and cook until tender, about 5 minutes. Remove the beans with a slotted spoon and transfer to the ice water to stop the cooking. Let cool in water, then drain and pat dry.
Whisk the egg and milk in a shallow bowl. Put 1/2 cup flour in another shallow bowl. Combine the breadcrumbs, the remaining 1/2 cup flour, the onion powder, garlic powder, cayenne and salt and pepper to taste in another bowl.
Line a baking sheet with parchment paper. Toss the green beans in the flour and shake of excess. One at a time, dip the beans in the egg mixture, dredge in the breadcrumb mixture and lay on the prepared baking sheet. Freeze until the coating is set, about 30 minutes.
Heat 3 inches oil in a deep pot over medium heat until a deep-fry thermometer registers 350 degrees. Fry green beans in batches until golden brown, 1 to 2 minutes. Transfer the beans with tongs or a skimmer to a rack or paper towels to drain. Serve with dip.