Season yogurt with lemon juice, parsley and salt. Allow 30 minutes in the refrigerator.
Grate potatoes and zucchini, place in a bowl and mix well with the flour. Stir in eggs and season with rosemary, oregano, nutmeg, salt and pepper. Mix well dough. Heat oil in a pan and put 3 tbsp. of the dough as heaps into the hot oil, flatten and fry per side for a few minutes until they are golden brown. Drain on paper towels.
Spread salmon on the plates, drizzle with a little olive oil and sprinkle with pepper. Serve with rösti and a yogurt.