Combine mustard, vinegar, sugar and salt and pepper to taste in a bowl. Slowly whisk in olive oil, and then stir in tomatoes and dill. Cover and reserve until salmon is cooked.
Cook lettuce leafs in boiling water 20-30 seconds, just until slightly wilted. Remove and cool in ice-cold water. Drain well, and pat dry. Place leaves, spread out and outer-side down, on a work surface. Place a salmon fillet in the centre of each leaf. Season with salt and pepper. Fold over edges of the leaves to seal in the salmon. Place fold side down in a large baking dish. Pour in enough water just to cover the bottom. Cover and bake in preheated 425 degrees F oven 12-15 minutes. Salmon can also be steamed. Divide salmon among 4 plates. Spoon over vinaigrette and serve with seasonal vegetables.