Heat 2 tablespoons of olive oil in a 12-inch skillet on low heat. Add the shallots and cook until they are clear in color. Add white balsamic vinegar, lemon juice and cook until the liquid has almost evaporated, about 10 minutes on medium high heat. Empty into a bowl and store in the fridge while you prepare the salmon.
Cut the salmon into 1 inch pieces (be sure the bones are removed) and add to food processor. Grind the salmon for 30 seconds. You should be able to form patties with the salmon; if not, grind for another 10 seconds.
Add the salmon to the prepared mixture. Mix in the bread crumbs. Beat the egg, add it to the salmon. Add the dill and pepper and form the salmon into 4 large patties.
Heat the remainder of the olive oil in a large non-stick skillet. Once the oil is hot add the patties and cook on medium high heat until golden brown. This should be about 2-3 minutes on each side.
Wash and dry the watercress and place equally on 4 plates. Add a salmon burger, pan juices and serve with tzatziki on the side.
Nutritional information per serving: 438 calories, 26 g fat, 5 g saturated fat, 89 mg cholesterol, 227 g sodium, 18 g carbohydrates, 1 g fiber, 35 g protein.