Season the fish with salt and pepper. Drizzle a little of the oil into a roasting tin. Add the fish, spacing the pieces slightly apart, and brush with the remaining oil. Scatter the pine nuts and raisins into the tin.
Bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 20 minutes or until the fish is cooked through.
Scatter the garlic into the roasting tin. Pile the spinach on top of the fish, making sure all the water has been thoroughly drained off the spinach first. Season lightly with salt and pepper and return to the oven for a further 5 minutes until the spinach has wilted.
Pile the spinach on to warmed serving plates and lay the fish on top. Spoon the pine nuts, raisins, garlic and cooking juices over the fish. Serve with lemon or lime wedges to squeeze over the fish and warmed rustic bread.