Bring the water and sugar to the boil in a pan. Add the rhubarb, cover and simmer over a low heat for approx. 5 mins. until just soft.
Place the cheese on top of the slices of bread, top with the rhubarb. Drizzle with oil, season.
Approx. 5 mins. in an oven preheated to 200 °C (convection).
Boil the sugar and water in a pan without stirring. Reduce the heat and simmer, swirling the pan occasionally until a light brown caramel has formed. Remove the pan from the heat, add the nuts and sesame seeds, mix, transfer to a sheet of baking paper, leave to cool, roughly chop.
Scatter the caramelized nuts and micro greens on top of the crostini.