Prepare a bowl of ice and water for an ice bath. Heat the water and wine, with the lemon half, in a medium saucepan until boiling. Add 2 tablespoons salt. Reduce heat to low (liquid should not even be simmering). Add shrimp; poach until just cooked through, 2 1/2 to 3 minutes. Transfer to ice bath to stop the cooking. Drain, and refrigerate until ready to assemble.
Trim ends from cucumber, and cut into two 5-inch pieces. With a mandoline, shave 1/16-inch-thick lengthwise strips from cucumber. Drizzle with olive oil in a shallow bowl; season with 1/2 teaspoon salt and the red-pepper flakes. Wrap each shrimp with one slice of cucumber, sprinkle with pepper, and serve.