Preheat the oven to 180˚C. Wrap each sweet potato in foil. Place on an oven tray and bake for 45-55 mins, depending upon size of sweet potatoes, until tender.
In the meantime, pour the contents of the Knorr Three Cheese packet into a jug. Fill up to the 250 ml mark with rapidly boiling water, stir with a whisk for 1 minute (alternatively use a fork).
Quickly blanche the spinach in rapidly boiling water. Drain well and press any extra liquid out using your hands, return to the pan. Add the Knorr Cheese sauce to the spinach in the pan and mix trough.
Remove the sweet potatoes from the oven, remove the foil, and cut a pocket in each sweet potato, lengthways. Season with salt and divide the sauce among the sweet potatoes. Top with the grated cheese and place back into the oven until the cheese is melted and golden. Serve immediately.