To prepare dressing, combine first 6 ingredients in a bowl, stirring well with a whisk.
To prepare fish, heat canola oil in a large nonstick skillet over medium-high heat. Sprinkle fish evenly with salt and pepper. Add fish to pan; cook 3 minutes on each side or until fish flakes easily when tested with a fork or until desired degree of doneness.
Arrange 1 cup greens on each of 4 plates. Top each serving with 1 fish fillet; drizzle with 2 tablespoons dressing.