Saute the onion in half the oil until softened and golden. Add the garlic and cook until soft. Cool.
Place the beans in a food processor with the parsley, add the cooled onion mixture and whizz to a paste. Add the yogurt, lemon juice and remaining oil and whizz again. Season to taste.
Serves 6-8 as a starter.
You can make this from fresh or frozen beans. Just make sure you hull them to keep the colour greenish. Serve as a dip with slices of pita bread.