Cut the rhubarb into 3/4 inch chunks and place in a pan with the sugar and ginger. Pour in 2 cups water and bring to the boil. Reduce the heat, cover and simmer gently for 10 minutes,until the rhubarb is very soft and pulpy.
Meanwhile,sprinkle the gelatin over 2 tbsp cold water in a small heatproof bowl. Leave to stand, without stirring, for 5 minutes,until the gelatin has become sponge like in texture. Set the bowl over a small pan of hot water and simmer,stirring occasionally, until the gelatin is dissolved completely into a clear liquid. Remove from the heat.
Strain the cooked rhubarb through a fine sieve into a bowl. Stir in the dissolved gelatin until thoroughly mixed. Leave to cool slightly before pouring into serving glasses. Chill at least 4 hours or overnight,until set.