Place the flour, sugar, yeast, salt and lemon zest in a large bowl or the bowl of a stand mixer fitted with a dough hook. Mix to combine.
Add the lukewarm milk and mix to form a rough dough. Knead until it forms a smooth ball.
Add the softened vegan butter. Continue to knead until the butter is fully incorporated and the dough is smooth and elastic. It may seem greasy and messy at first but keep kneading and I promise you the butter will all mix in and the dough will become smooth.
Once the butter is fully incorporated the dough should look smooth and silky and it should pull away from the sides of the bowl cleanly. It should still be soft and slightly sticky but if it seems too wet then you can knead in a little more flour; be careful not to add too much however.
Place the dough in a lightly oiled bowl, cover and set aside to rise in a warm spot until doubled in size, about 1 hour.
Punch down the risen dough and give it a brief knead to knock out any air bubbles.
Roll it out on a lightly floured surface into a rectangle about 30 x 40 cm (12 x 16 in).
Spread the lemon curd evenly over the surface, leaving a border of about 1cm around the edges. Scatter over the sultanas.
Starting at one of the short edges, roll the dough up fairly tightly into a sausage. Brush the end with a little water to help seal the roll.
Use a very sharp knife or a length of floss to trim the ends off the roll to kneaten it, then slice it into 12 rounds.
Place them spaced apart on two baking parchment lined baking sheets. Loosely cover and set aside to rise for about 45 minutes, until doubled in size.
The buns are ready to bake when they look puffy and if you gently press some of the exposed dough with a finger it springs back slowly most of the way but leaves a small indentation. If it springs back quickly and fills in completely then it isn't ready yet.
While the buns are rising, preheat the oven to 200°C/180°C fan/400°F/gas mark 6.
Gently brush the buns with milk then bake for 10 minutes. Turn the oven down to 180°C/160°C fan/350°F/gas mark 4 and bake for another 10 minutes until deep golden. If you have a probe thermometer the internal temperature should reach 90°C/195°F.
Transfer the buns to a wire cooling rack and allow to cool completely.
To make the icing, sift the icing sugar into a bowl and gradually stir in enough lemon juice to form a thick but spreadable icing.
Spread some of the icing over the top of each bun using the back of a spoon. Top with a glace cherry half and serve asap.