In a saucepan, combine the poaching liquid ingredients and bring it to a boil over high heat, then turn to a simmer and cook 6 minutes till the carrots are tender. Remove from the heat and cover to keep warm.
In a 10-inch sauté pan, place the salmon fillets without touching each other. Pour the hot poaching liquid over the salmon and bring it to a simmer over medium heat. Cook for just 3-4 minutes. The salmon will still be pink and rare.
Turn off the heat and let sit in the liquid about 10 minutes to gently finish cooking. Chill in the poaching liquid for at least an hour, then transfer the salmon carefully (a fish spatula is slotted and pretty thin) to a serving platter and keep covered and chilled till ready to serve.
To prepare the topping, julienne or shred the cucumber; use a Japanese mandoline if you have one. Otherwise shred it trough the blade of a food processor or box grater on the biggest holes. You want to end up with about 2 cups shredded.
In a bowl combine it with the yogurt, fresh dill and season it to taste with salt and pepper. Spoon that on top of the salmon and serve.