Drizzle each sole fillet with 1 tsp lemon juice, 1 tsp soy sauce, 1/2 tsp ginger, and a light, even drizzle of sesame oil. Gently roll the fillets lengthwise and arrange them on a heatproof plate.
Fill a large saucepan fitted with a steamer with 1in (2.5cm) water; bring to the boil, then reduce the heat to a simmer.
Blanch the bok choy leaves for several seconds in the water, or until soft, then place them briefly into a bowl of iced water.
Wrap each fillet in 4–5 leaves, securing with cocktail sticks if necessary. Set the plate with the fish on the steamer rack, place the lid on the steamer, and steam for 8–10 minutes, or until the fish becomes opaque.