For the spatchcock poussin, preheat the oven to 230C/450F/Gas 8.
Remove the backbone from one of the birds by carefully pushing a knife into the bottom-end of the bird until you see the point of the knife emerge at the neck. Push the knife down against one side of the spine, cutting through the rib cage. Open up the bird and cut away the spine at the other side.
Place the bird, skin-side down, onto the chopping board. Break the breast bone by hitting it with your hand (this will flatten the bird so that it grills more easily).
Turn in the legs of the bird so that it looks like it's cross-legged.
Make a hole in the loose skin connecting the legs of the bird to its body. Hook the ends of the legs into these holes. Tuck the wings under the body of the bird. Repeat with the other bird.
Marinade in a bowl of the garlic, rosemary, lemon and olive oil. If easier, you can skewer each bird to hold it in place.
Marinade at least for one hour.
Heat a grill to hot, put the poussin skin-side down on a tray under the grill and leave to cook for three minutes.
Turn over the meat and give it a further 30 seconds. The transfer to the oven for eight minutes to finish cooking. Check the bird is cooked through by piercing the meat in the thickest part and checking the juices run clear, then remove from the grill and rest until needed.
For the couscous salad, dissolve the stock cube in 180ml/6fl oz of boiling water in a jug and add the olive oil.
Put the couscous in a bowl and pour the boiling water over. Cover in cling film and leave to stand for five minutes.
Fluff up the couscous with a fork, then add the pepper, herbs, chilli, zest and salt and pepper, to taste.
Place the couscous in a serving bowl and then put the quail and any meat juices on top to serve.