1. Heat a large nonstick skillet over medium-high heat. Add 2 teaspoons canola oil; swirl to coat. Sprinkle fish with salt. Add fish to pan; cook 4 minutes on each side or until desired degree of doneness. Remove fish from pan; keep warm.
2. Combine remaining 2 tablespoons canola oil, miso, and next 4 ingredients (through sesame oil) in a large bowl; stir with a whisk. Add cucumber and spinach to bowl; toss well. Arrange 1 fillet and 2 cups salad on each of 4 plates. Sprinkle each serving with 1/4 teaspoon sesame seeds.