Heat the olive oil in a saucepan, sauté the onions, add the spinach, pour the stock and simmer for 10 minutes while stirring. Cook the spaghetti in salted water for 8-10 minutes al dente, drain. Season the spinach with salt, pepper, nutmeg and oregano. Crumble the sheep`s cheese and mix it with the spinach, let simmer for another 5 minutes. Add lightly roasted pine nuts, season to taste. Pour the sauce over the spaghetti.