Cut each of the salmon slices into 18 thin strips, about 1/2 to 1-inch wide. Roll each strip as tightly as possible to make a rose, and place them on a plate. Cover lightly with plastic wrap and set aside in the refrigerator.
On a clean dry surface, carefully slice the eggs in half lengthwise. Very gently remove the yolks from each egg half and add them to a medium-sized mixing bowl.
Spread out the "handful" of fresh dill sprigs on a large serving platter and then arrange the egg white halves on top. (The dill will keep them from wobbling.)
Use a fork to mash the yolks, and then add the sour cream. Mash until you don't see any lumps from the yolks. Then add 2 tablespoons of the onion, tomato, chopped capers, 1 tablespoon of dill, mayonnaise, mustard, lemon juice, salt pepper and cayenne. Mix until everything is evenly incorporated.
Add the yolk mixture to a large zip-lock bag and then cut about 1/4-inch off one of the bottom corners, to turn it into a pastry bag. Gently squeeze the mixture evenly among each of the 18 egg white halves. Sprinkle the remaining 1 tablespoon of onion on top of each one.
Remove the salmon "roses" from the refrigerator and carefully place one on top of each deviled egg, using a bit of pressure so that it's partially inserted into the yolk mixture. Add 1 caper and 1 tiny dill sprig to the center of each salmon rose, and then sprinkle them with the lemon zest.