Coarsely chop the walnuts and roast them in a pan without fat until golden brown. Wash parsley, shake dry and chop the leaves coarsely. Peel garlic and chop coarsely. Puree parsley, garlic and nuts in a blender.
Add oil, up to 6-8 tablespoons, little by little.
Cut the chilli lengthwise, remove the seeds and cut into very thin rings. Grate cheese finely. Stir cheese and chilli into the pesto. Season pesto with salt and pepper. Pour into clean screw-top jars with lids.
Add the rest of the oil each time so that the pesto is well covered. Close the jars. Keeps in the fridge for 3-4 weeks. (Attention: Becomes more and more spicy because of the chilies!).