Place couscous in a shallow dish and cover with 300ml of boiling water; cover the dish with clingfilm and set aside for 5 minutes.
Cut 'lids' off the tops off the peppers and scrape the seeds out from inside; place the peppers and their lids in a large saucepan and cover with boiling water; cook the peppers for 5 minutes, drain and set aside to cool.
Heat the oil in a large frying pan, add the cumin seeds, coriander and cayenne pepper and fry for a few seconds before adding the onion and garlic; fry gently for 3-5 minutes until the onion is transparent.
Add the tomatoes, chickpeas and green beans, stir to mix and fry for a further 2-3 minutes; stir in the couscous and remove from the heat.
Stand the peppers up in a shallow dish, fill the pepper cavities with couscous mix, put on their lids; bake for about 35-40 minutes.