Roasted Onions: Preheat oven to 425 degrees F.
Combine all of the ingredients, except the onions in a medium shallow baking dish. Add the onions, toss them in the mixture and season with salt and pepper, to taste.
Cover the onions with foil and roast for 20 minutes. Remove the foil and continue roasting until tender, about 35 to 40 minutes, basting with the juices several times. In a saute pan place butter and melt. Add orzo and tomatoes. Toss until orzo is cooked through. Place the orzo in a large bowl and spoon the onions and the cooking liquid over the pasta.
Tapenade: Place all ingredients in a food processor and process until smooth. Season with salt and pepper, to taste.
Salmon: Season the salmon with salt and pepper to taste. Spread 2 tablespoons of the tapenade over each piece of salmon (not on the skin side). Heat 2 tablespoons of olive oil in a large saute pan. Place 4 of the fillets in the pan, tapenade side down, and saute until a crust forms, about 2 minutes. Turn the fish over and continue cooking for about 5 minutes for medium-rare doneness.
Serve the salmon with the Roasted onions.