Roughly chop the walnuts by giving them a few pulses in the food processor. I like to leave them in fairly large chunks. Pour into a bowl and set aside.
Add olives, garlic and spices (chili, cumin, coriander, oregano and sumac) to the bowl of the food processor and process for a few seconds until the olives and garlic are finely chopped. Add oil and lemon juice and process for a few seconds more to combine. Transfer the mixture to a bowl. Stir in walnuts and parsley. Season to taste with salt and fresh ground black pepper.