Sift 1 2/3 cups (230g) of the flour into a large bowl and add 1/3 cup (75g) of the caster sugar and the yeast, then mix well. Heat the milk and 3 tbsp of the spread in a small saucepan until lukewarm. Stir into the flour mixture. Stir in the egg. Add another 1 1/4 cups (175g) flour and stir vigorously for 2–3 minutes or until the dough pulls away from the side of the bowl.
Dust a work surface with the remaining flour. Turn out the dough and knead for about 10 minutes or until smooth and elastic, working in enough flour to keep it from sticking. Coat a large bowl with cooking spray and put in the dough; turn to coat. Cover with a damp tea towel and rest for 10 minutes.
Meanwhile, line a baking tray with baking paper. Toss the walnuts and sultanas with the remaining caster sugar and 1 tbsp orange zest; set aside. Melt the remaining spread; set aside. Place the dough in the baking tray and pat into a 35 x 23cm oval.
Brush the dough with the melted spread. Score the dough lengthways into three equal sections without cutting through. Turn the tray so one long edge of the dough is facing you. Working within the section closest to you, score a mark every 2.5cm along the edge of the dough, then cut strips 7.5cm long and 2.5cm wide. Turn the tray around and repeat on the other side. Spread the walnut filling down the centre. Fold the strips over the filling and seal the ends well. Cover with a towel. L ave to rise in a warm place for about 45 minutes or until almost doubled in size.
Meanwhile, preheat the oven to 190 degrees C. Bake the bread for about 20 minutes or until golden. Cool on a wire rack for 15 minutes. Meanwhile, stir the icing sugar with the remaining orange zest and enough orange juice to make an icing that will coat the back of the spoon. Drizzle over the warm bread. Serve warm or allow to cool to room temperature.