Finely grate the rind of 2 of the limes and halve these limes. Mix the rind with the ginger and coriander in a non-metallic bowl and stir in 1 teaspoon of the oil to make a rough paste.
Carefully lift the skin from the chicken legs and push under the ginger paste. Pull the skin back into place, then cut 3–4 slashes in the thickest parts of the legs and brush with the remaining oil.
Put the legs in a roasting tin, flesh-side down, with the halved limes and cook in a preheated oven, 220°C (425°F), Gas Mark 7, for 45–50 minutes, basting occasionally. The legs are cooked when the meat comes away from the bone and the juices run clear.
Meanwhile, put the rice in a pan with 400 ml (14 fl oz) cold water, cover with a tight-fitting lid and cook over a medium-low heat for 10 minutes until the water has been absorbed and the rice is almost cooked. Set aside somewhere warm until the chicken has finished cooking.
Spoon the rice into small bowls to mould, then turn it on to serving plates. Add the chicken legs, squeeze over the roasted lime and scatter with coriander leaves. Serve immediately with the remaining lime, cut into wedges.