Cook the pasta according to the packet instructions, drain and keep warm.
Meanwhile, gently fry the garlic and chilli (if used) in the oil for a few seconds, then add the spinach and half of lemon juice and a spoonful of the pasta’s cooking water. Put a lid on and sauté for about 5 minutes over low heat.
When the spinach has wilted, transfer it to a small food processor, add the nuts, herbs and the remaining lemon juice together with a couple of pinches of grated lemon zest. Blend for a few seconds, then add the feta and whiz again until you get a slightly textured sauce. Season with salt and pepper to your liking. Add more lemon zest, if needed.
Add the feta & spinach sauce to the pasta, then toss well.
Serve warm, garnished with extra pine nuts and some crumbled feta.