Bring a medium saucepan of water to the boil and add the potatoes. Cook for 10 minutes to par-boil. Remove potatoes from water and allow to cool. Grate potatoes into a large bowl and use clean hands to mix in the spring onions, half the dill, salt and pepper to work the starch in the potatoes.
Heat a large non-stick frying pan over medium high heat. Divide potato mixture into four equal rostis. Add half the olive oil then add each rosti to the pan. Cook for 2-3 minutes each side or until golden brown.
Toss zucchini in a small bowl with the lemon juice, remaining olive oil and dill.
Use an egg slide to place a rosti onto each serving plate. Top with shaved zucchini, a dollop of crème fraiche, smoked salmon and sprinkle over capers.