To make the sauce, place all the ingredients in a small bowl and mix well. Season to taste.
Drain the beans and place two thirds of them in a saucepan with fresh cold water. Bring to boil and simmer for 20 minutes, until tender. Drain when cooked.
Meanwhile place the remaining uncooked beans in a food processor and pulse until smooth.
Transfer to a bowl and place the cooked beans in the processor. Add garlic, spring onion, parsley, cumin, mint, green chilli, coriander and baking powder and blitz to a puree.
Mix well and season with salt and pepper.
Add the uncooked pureed beans to that mixture and mix again. Shape into balls no larger than a walnut and flatten each into a smallish disc, about 2 cm thick.
Have the oil really hot in a frying pan and drop the falafel disks gently into the pan, just few at a time to cook about 6-8 minutes, turning until evenly browned on all sides.
Remove with a slotted spoon onto kitchen paper and drain, then arrange on a serving plate and pour some tahini sauce over them. Serve warm.