For the chermoula, purée all the ingredients, except the olive oil, in a food processor. With the motor running, add the oil slowly to make a wet paste.
Place the lamb in a dish, add half the chermoula paste and rub all over the lamb. Stand for 1 hour.
Heat the olive oil in a frying pan with a tight-fitting lid over high heat. When hot, fry the lamb for 5 minutes (this may need to be done in batches) until it is well coloured. Add the pumpkin, the remaining chermoula paste, lemon juice, honey, sea salt to taste and 750 ml (26 fl oz/3 cups) water. Bring to the boil, then reduce the heat to low, cover and simmer gently for 1½ hours or until the meat is tender. Fold in the chickpeas to warm them.
To prepare the couscous, place the butter, olive oil and 400 ml (14 fl oz) boiling water in a bowl with a pinch of salt. Cover with foil and stand for 2 minutes or until the butter has melted. While stirring, add the couscous, and when the liquid is absorbed, fluff with a fork.
Transfer the couscous to a basket steamer lined with a tea towel (dish towel) or muslin (cheesecloth). Set over a saucepan of boiling water and steam for 20 minutes, or until tender.
For the orange salad, juice 1 of the oranges, then peel and segment the remaining oranges. Combine all the ingredients and refrigerate until chilled.
To serve, place some couscous into each of four bowls, spoon the tagine on top and serve with the orange, almond and chopped date salad on the side.