1.Melt half of the butter in medium frying pan, cook onion and chorizo, stirring, until onion softens. Cool 10 minutes. Combine chorizo mixture in medium bowl with breadcrumbs, cheese, egg, parsley and nuts.
2.Preheat oven to 200°C (180°C fan-forced).
3.Wash chicken under cold water, pat dry inside and out with absorbent paper. Tuck wing tips under chicken. Trim skin around neck, secure neck flap to underside of chicken with skewers.
4.Fill cavity with chorizo mixture, fold over skin to enclose stuffing, secure with toothpicks. Tie legs together with kitchen string. Place chicken and lemon in medium baking dish, rub chicken all over with remaining butter. Roast, uncovered, about 1½ hours or until chicken is cooked through, basting occasionally with pan juices. Remove and discard toothpicks.
5.Meanwhile, place ingredients for spinach and red onion salad in large bowl, toss gently to combine.
6.Serve chicken with stuffing, lemon and salad.