Preheat oven to 190C. Combine the chickpeas and 2 tbsp of olive oil in a large roasting pan and bake, stirring once or twice until crisp and browned - about 20 mins. Beware! they can explode.
Sprinkle chickpeas with salt and pepper and remove from the pan with a slotted spoon. Keep warm.
Add the remaining oil to the pan with the lamb. Break it up a bit and roast until it is no longer pink and has cooked dry. Stir and continue to break up until it is crispy.
Stir the onion, green beans, garlic, orange zest, cumin and cayenne into the lamb. Sprinkle with salt and pepper. Return the roasting pan to the oven and roast until the vegetables are tender and browned, the lamb is very crisp and the spices are fragrant - 10 to 15 mins.
Remove the pan from the oven, stir in the chickpeas and transfer everything to a serving dish.
Put the roasting pan on the stovetop over a medium heat. Add the orange juice and cook, stirring and scraping up any brown bits on the bottom of the pan, until warm and slightly thickened - 5 to 10 mins. Drizzle this over the chickpea mixture and garnish with parsley to serve.