Soak cedar shingles in water for 2 hours. Dry briefly, then coat the cooking side of the shingle with canola cooking spray.
Place salmon fillets on the cedar shingles and bake at 425 degrees for 10-15 minutes, depending on the thickness of the salmon (about 10-12 minutes per inch at the thickest end).
Meanwhile, chop blanched watercress and add it to an 8-cup measure or medium sized bowl, along with the green onions, yogurt, dill, sour cream, half-and-half or milk, Worcestershire sauce, Dijon mustard, black pepper and salt.
Serve each salmon filet with a healthy dollop of the watercress yogurt sauce.
This recipe was inspired by Judson Simpson, executive chef for the House of Commons in Canada