Lightly cook salmon, after thawing if frozen. An easy way is to poach in very hot but not boiling water for about 4-5 minutes. Do not cover salmon with water, only allowing water to be about half way up the fillets. Set aside.
Put egg in bowl, lightly beat. Mix in 1 tbsp horseradish, lemon zest, lemon juice, scallions, breadcrumbs, tsp of salt and 1/8 tsp pepper. Mix evenly.
In another bowl, break up salmon into small pieces/flakes.
Pour egg mixture from step two on to of salmon, and mix until salmon is thoroughly covered with mixture.
Cover glass or similar dish with foil (saves on cleanup!). Make four similarly-sized balls of this salmon mixture using your hands and space evenly on the dish.
Press each ball into a patty of about 3.5in in diameter and 1 inch thickness.
Cover the dish and the salmon patties and place in fridge for at least 30 minutes. This helps the patties maintain their shape.
While patties are in fridge, mix yogurt, dill, salt, pepper and 1 tbsp horseradish (to taste) in a small bowl to make sauce. Cover and refrigerate. The longer this sauce is in the fridge, the stronger the dill flavor.
Remove patties from refrigerator.
Heat a pan or skillet to medium to high heat. Pour a small amount of olive oil in the skillet, and when hot place patty or patties (can do one one or more at a time depending on your comfort level) in pan.
Let sizzle until brown on one side, and then flip. If you made the patties well and refrigerated them, flipping should be easy.
When brown on both sides, place on bun of your choice, toasted or prepared however you like (I like to brush bun with olive oil, parmesan cheese and hot pepper before toasting in convection oven).
Cover with yogurt dill sauce, and add lettuce, tomatoes, etc. Serve immediately.