Start this salad 4-6 days before you want to serve it. Put each of the beans in a bowl, cover with water and leave to soak overnight. Drain and put each variety into a wide-neck jar. Cover with muslin, secure with elastic bands and place all the jars in a warm, dark place such as an airing cupboard.
Twice a day, fill the jars with water, drain through the muslin to rinse the beans. The beans will have sprouted in 4-6 days. Remove the sprouted beans from the jars and rinse again.
To make the dressing, beat all the ingredients together in a bowl until the honey is evenly blended. Slice the onion and mix with the sprouted beans. Place in a serving dish and add the dressing. Toss the salad until all the sprouts are coated and serve immediately.