Butterflied leg of lamb with Harissa and chickpea salad

1 butterflied leg of lamb (1.5kg approximately)

100g harissa

zest and freshly squeezed juice of 2 lemons

For the chickpea salad:

700g dried chickpeas

2 tbsp extra virgin olive oil

4 onions, sliced

4 garlic cloves, chopped

For the dressing:

175ml extra virgin olive oil

50ml freshly squeezed lemon juice

2 garlic cloves, crushed

2 tsp ground cumin

salt

pepper

To serve:

3 tbsp coriander, chopped

3 tbsp flat leaf parsley, chopped

150ml natural yoghurt