1.Heat oil in tagine or flameproof casserole dish, cook onion and garlic, stirring, until onion softens. Add spices, cook, stirring, about 1 minute or until fragrant. Add tomato, cook, stirring, about 5 minutes or until tomato softens. Bring to the boil. Reduce heat, simmer, stirring occasionally, 10 minutes or until sauce thickens slightly.
2.Meanwhile, shell and devein prawns leaving tails intact.
3.Add prawns to pan, cook, covered, stirring occasionally, about 5 minutes or until prawns are changed in colour. Season.
4.Combine herbs, nuts and preserved lemon in small bowl.