In a blender, combine soy sauce, 1 tbsp. lemon juice, the sugar, fresh and powdered ginger, and red pepper flakes and blend to combine. With the machine running, slowly pour in canola oil and continue blending until emulsified, about 30 seconds. Spread asparagus on a rimmed pan, pour half the marinade over it, and toss to coat. Reserve remaining marinade.
Prepare a gas or charcoal grill for direct high-heat grilling (450° to 550°; you can hold your hand 5 in. above cooking grate only 2 to 4 seconds). Rinse fish; pat dry. Season on both sides with salt and pepper and drizzle with olive oil and the remaining lemon juice.
When grill is ready, lightly oil the cooking grate and put fish on grate skin side down. Grill 3 minutes, then turn and continue grilling until fish is no longer translucent inside (cut to test), 2 to 3 minutes longer. Transfer to a clean plate and tent with foil to keep warm.
Grill asparagus spears, turning once or twice, until tender and browned, about 5 to 6 minutes. Divide fish among 6 plates and top each with several asparagus spears. Use a spoon to drizzle with some of the reserved marinade.
Nutritional analysis is per first-course serving.