Place the plums with the sugar and water in a pan, cover and simmer over a low heat for approx. 5 mins. until almost soft, allow to cool and pour into the glasses.
Combine the mousse powder, water and Lebkuchen spice and stir until the powder has dissolved. Carefully fold in the whipping cream. Divide the mousse onto the plums, cover and chill for at least 1 hr. Scatter with the almonds.