Wash the rhubarb and cut into small pieces. Mix with the sugar and 3 tbs water in a pot and steam for around 10 minutes at low heat.
Then sieve the rhubarb and collect the juice. Dissolve the yeast in the warm juice.
Mix the flour and salt. Add the oil and the juice and knead everything together. Cover with a kitchen towel and let rise for about 1 hour.
Prepare a floured countertop. Knead the dough once again and roll out into an approx. 10x11in long rectangle. Cut into three equally thick pieces. Spread 2/3 of the almonds and the rhubarb on every piece. Start with the long side and roll up the dough pieces and press together.
Braid the three ropes into a bun and put onto a baking tray with parchment paper. Coat the bun with some water and sprinkle with the remaining almonds. Let rise for another 20 minutes. Meanwhile, preheat the oven to 180°C/360°F.
Bake in the middle of the oven 160°C/320°F for 45-50 minutes. If your bun seems to get too dark, cover with aluminium foil in the last third of the baking time.
When cooled down, serve with powdered sugar on top.