Onions peel, halve and in fine strips cut. Clean the spinach. Wash and halve the tomatoes. Mix everything together. Season vinegar with salt, pepper and sugar, fold in oil. Fold into the salad. Put it in a cold place.
Whisk eggs and milk. Season with salt and pepper. Heat 1/2 tbsp. oil in a coated frying pan. Fry 1/4 of the egg mixture in it over a low to medium heat for about 5 minutes. Remove the omelette from the pan and keep warm. Do the same with the remaining oil and egg mixture.
Arrange omelettes on plates, fill with salad and cover with smoked salmon. Sprinkle with coarse pepper.