Meanwhile, soak the bread in the milk or stock. Put the walnuts, garlic and some salt in the container of a food processor, and pulse to grind coarsely. Gently squeeze some liquid from the bread, and add the bread to the container, along with the oil. Process until combined but not puréed. Add as much of the remaining milk or stock as necessary to give the mixture a mayonnaise-like consistency. By hand, add the paprika or chili powder, and stir in the parsley if you are using it. Taste and adjust seasoning as necessary.
03Serve the chicken hot or at room temperature with the sauce spooned over it.