Prepare barbecue (medium-high heat). Whisk soy sauce, mirin, lemon juice, oil, ginger and lemon peel in shallow bowl to blend. Add shrimp and stir to coat; let marinate 10 minutes.
Drain marinade into small saucepan and boil 1 minute. Grill shrimp until just opaque in center, turning occasionally, about 3 minutes.
Divide bok choy between 2 plates and drizzle with some of warm marinade. Top with shrimp. Serve, passing remaining marinade as sauce, if desired