Cook the spaghetti according to the package instructions.
Dry-fry the pine nuts in a frying pan. Put a few aside for decoration.
Crush the garlic with a pestle & mortar with a pinch of salt. Add the mint leaves and the pine nuts, grind to coarse paste.
Crumble in the feta, then drizzle the oil gradually until you get a thick paste, while pressing and stirring with the pestle. Season to taste.
Drain the pasta and toss with the paste, sprinkle with the pine nuts and scatter a few mint leaves over it.
Serve warm with a squeeze of lemon juice.