Bring the vinegar, sugar, cumin seeds and salt to a boil in a saucepan; then, lower the heat and simmer, stirring occasionally, for about 5 minutes. Add sliced onion and simmer, stirring occasionally, for 2 minutes. Transfer to a bowl or mason jar and cool completely. Add a sprig of dill. Refrigerate pickled onions and use within a week.
Bring a large saucepan of water to a boil over medium-high heat. Using a slotted spoon, carefully lower eggs into water one at a time. Cook 6½ minutes, adjusting heat to maintain a gentle boil. Transfer eggs to a bowl of ice water and chill until just slightly warm, about 2 minutes. Gently crack eggs all over and peel, starting from the wider end, which contains the air pocket.
Cut bread into thin slices and lightly toast. Smear toasts with soft cheese of your choice. Layer on smoked salmon and top with pickled onion. Cut eggs into fourths lengthwise and add to the toasts. Garnish with fresh dill and enjoy.