Rinse the aduki beans and add to a pan with the khombu and 3 cups of water. Bring to the boil then reduce to simmer for 15 - 20 minutes until tender. Drain, discard the khombu and set the beans aside to cool.
Steam the sweet potato for 5 minutes until tender. Combine the onion with the aduki beans and sweet potato.
Mix together the olive oil, brown rice vinegar, mirin and soy sauce and bruised garlic clove. Toss the dressing through the salad and set aside to absorb the flavours. Remove the garlic clove before serving.
Tip: adding a strip of khombu to the cooking water helps to improve the digestibility of the bean. Khombu is available from health food stores and Asian grocers.