Mix the breadcrumbs with the parsley, garlic, lemon zest, salt and pepper, then add butter and lemon juice. Mix thoroughly with your fingers.
Place the cod in a shallow, ovenproof dish and press the buttered crumbs firmly onto the cod to form an even crust. Bake at 220C/200C Fan/Gas 7 for 20–25 minutes until the crust is browned and the fish just cooked through. Serve immediately.