1. In 26-inch fish poacher* over high heat (the poacher will require 2 heating units), heat first 7 ingredients to boiling.
2. Rinse salmon with running cold water. Place salmon on poaching rack; lower rack with salmon into boiling liquid in fish poacher; over high heat, heat to boiling. Reduce heat to low; cover and simmer 40 minutes or until fish flakes easily when tested with a fork. Remove rack from poacher. Using 2 pancake turners, place salmon on large platter; cover and refrigerate until well chilled, about 2 1/2 hours.
3. Meanwhile, prepare Cucumber Mayonnaise; cover and refrigerate.
4. To serve, with knife or kitchen shears, carefully cut off skin from top half of salmon. Thinly slice lemons and cucumber; arrange lemon and cucumber slices overlapping slightly, on platter with salmon. Spoon 1/2 cup Cucumber Mayonnaise in narrow lengthwise strip on top of salmon. Arrange fresh herbs on sauce. Serve with remaining mayonnaise.