Put the flour and 1 tsp salt into a large bowl. Make a well in the centre and add the yeast. Meanwhile, warm the milk and butter in a pan until the butter melts and the mixture is lukewarm. Add the milk mixture and egg to the flour mixture and stir until the contents come together as a soft dough (add extra flour if you need to).
Tip the dough onto a well-floured surface. Knead for 5 mins, adding more flour if necessary, until the dough is smooth, elastic and no longer sticky.
Lightly oil a bowl with the vegetable oil. Place the dough in the bowl and turn until covered in oil. Cover the bowl with cling film and set aside in a warm place for 1 hr or until doubled in size. Lightly grease a baking sheet and set aside.
For the filling, knock the dough back to its original size and turn out onto a lightly floured surface. Roll it into a 1cm-thick rectangle. Brush all over with the melted butter, then sprinkle over the sugar, cinnamon and fruit.
Roll up the dough into a tight cylinder, cut into 9 x 4cm slices and position on the prepared baking sheet, leaving a little space between. Cover with a tea towel and set aside to rise for 30 mins.
Heat oven to 190C/170C fan/gas 5. Bake the buns for 20-25 mins or until risen and golden brown. Meanwhile, melt the glaze sugar with 4 tbsp water until syrupy.
Remove from oven and glaze. Set aside to cool on a wire rack. Once cool, mix the zest and icing sugar with about 2 tbsp water to drizzle over the buns. Serve.