Add the tomato and herb sauce to a large saucepan along with the chopped tomatoes, harissa paste and half the chopped parsley. Simmer over a low heat for 5 minutes, then add the falafels and chickpeas and simmer for a further 5 minutes.
Meanwhile, put the couscous in a bowl and pour over 275ml boiling water. Cover with clingfilm and leave for 10 minutes, then stir through the remaining chopped parsley.
Pierce the bag of garden vegetables and cook according to the instructions on the packet. Stir the cooked vegetables through the tagine and serve with the couscous. Garnish with the reserved sprigs of parsley and extra harissa.