Roast the pine nuts in a pan without fat until golden brown, take them out and let them cool down. Cook the pasta in 3-4 l boiling salted water (1 teaspoon salt per litre) according to package instructions.
Meanwhile grate the pecorino finely. Wash the lemon hot, dry it and grate the peel thinly. Halve the lemon and squeeze it. Wash parsley, shake dry, pluck off leaves and chop finely.
Approx. 2⁄3 of pine nuts finely crushed in a mortar.
Remove 4-5 tablespoons of the pasta cooking water. Mix with crushed and whole pine nuts, pecorino, lemon peel and juice, parsley and olive oil. Drain the pasta and put it back into the pot. Mix the sauce with the pasta, season to taste with salt and pepper.
Pluck the mozzarella, pour over it and serve immediately.