This is how I like to eat salmon patties in summertime. It's a light supper good for when the weather is super hot; a glass of white wine, dry rose or a lighter beer like a pilsner or lager is a good accompaniment. You can of course put the salmon patties on a bun and then have a real salmon burger. If you go this route, maybe top the patty with some cole slaw and some mayo or remoulade.
Either grind your salmon, the onion and the bread through the fine die of the grinder (how I do it), or pulse it a few times in a food processor. Put the mixture in a bowl and mix in the egg white, white pepper, salt, sour cream and dill. Form into patties. Put the patties in the fridge while you make the salad.
Toss the sliced fennel and red onion with a little salt and the lemon juice and let it marinate for 20 minutes. Cut the cucumber lengthwise and remove the seeds with a spoon. Slice it thinly and add it to the bowl with the fennel and onion. Stir in the pickled mustard seeds, black pepper, sugar and sunflower oil and set aside.
I like to grill my salmon burgers. Get your grill very hot and scrape down the grates with a wire brush. Dip a paper towel into some vegetable oil and use tongs to wipe down the grill grates. Set the salmon patties on the grill and cook with the grill cover up for about 3 minutes. Flip and grill for another 3 minutes or so.
When you are ready to serve, toss the watercress in with the rest of the salad and serve with the salmon patties. Top the patties with the salmon caviar if you have it.