Boil potatoes, drain, cool down and mash.
Blanch spinach shortly, drain and chop.
Mix potatoes with flour, yolk, olive and spinach.
Knead smooth, uniform dough. You may need more flour depending on what kind of potatoes you are using. Dough cannot be sticky.
Add salt and pepper.
Form small balls.
Cook gnocchi in salt water. Count 5 min starting from the moment when gnocchi will be afloat.
Meantime prepare sauce.
Heat oil, add garlic and onion, fry 2 min, add passata and sugar, simmer 10 -15 min.
Serve gnocchi on arugula, poured with tomatoes sauce and sprinkle with mozzarella.