To make sauce, whisk together in a small bowl yogurt, lemon zest and juice and dill, mixing well. Cover and refrigerate until ready to use, up to 1 day.
Toast muffin halves and place on 4 plates. Spoon a little lemon sauce on each muffin half and top with 2 salmon slices.
To poach eggs, fill a medium saucepan ⅔ full with water and bring to a simmer over medium heat. Add lemon juice. Crack 1 egg into a ramekin or a small bowl. Whisk the water to create a vortex, and gently pour egg into the spinning water. Repeat with remaining 3 eggs, one at a time, and gently simmer for 2 to 3 minutes. Using a slotted spoon, remove eggs, shake off any excess water and place on top of salmon.
Spoon more yogurt sauce over each egg, sprinkle with salt and pepper and garnish with dill. Serve immediately, with lemon wedges on the side.