Mix the rhubarb and sugar in a wide pan, bring to the boil, cover and cook for approx. 5 mins., puree, leave to cool. Set aside 2 tbsp.
Mix the flour, sugar, salt and yeast in a bowl. Add the milk, knead for approx. 10 mins. to form a soft dough, cover and leave to rise for approx. 1½ hrs. until doubled in size.
Mix the rhubarb puree, hazelnuts and coconut flakes. On a lightly floured surface, roll out the dough into a rectangle (approx. 35 x 45 cm).
Spread the filling on top, smooth down, leaving a border of approx. 1 cm all the way around. Starting from one of the long edges, roll up the dough. Cut the roll in half lengthwise, twist the strands with the cut sides facing up. Shape into a wreath, place in the cooking pot, cover with the lid.
Approx. 40 mins. on the bottom shelf of an oven preheated to 220°C. Remove the lid and cook for a further 5 mins. Remove from the oven, leave to cool on a rack.
Mix the icing sugar with the reserved rhubarb liquid, decorate the wreath with the icing.