Wrap the fish chunks in the pieces of pancetta. Using a sharp knife, cut a small cross in the base of each tomato. Thread the pancetta-wrapped cod, tomatoes, mushrooms and red pepper chunks alternately on to the soaked wooden skewers. Place in a shallow ovenproof dish.
Melt 25 g (1 oz) of the butter with the oil in a saucepan, stir in the lemon rind and season with a little salt and pepper. Brush over the kebabs and leave to marinate in the refrigerator for about 1 hour. Place the kebab dish on the upper rack of the halogen oven.
Set the temperature to 250°C (482°F) and cook the kebabs for 10–15 minutes, turning them once or twice, until cooked through.
Meanwhile, melt the remaining butter in the pan and stir in the garlic, parsley and thyme. Season lightly and serve spooned over the kebabs, accompanied by rustic bread for mopping up the juices.