Rinse the sweet potatoes and parboil in a little water for 15-20 minutes until they are almost tender. Drain and allow to cool.
Meanwhile, wash the spinach thoroughly.
Place the damp spinach in a hot pan, cover and allow to wilt for 1-2 minutes. Drain in a sieve. Season with salt, pepper and some nutmeg.
Mix the vinegar and oil to make a dressing, season with salt and pepper. Grate the Parmesan.
Grate the zest from the lime and squeeze the juice.
Mix the lime zest and juice with the maple syrup, sesame oil, tahini paste and soy sauce. Season with pepper and salt.
Halve the sweet potatoes lengthways, place on a baking sheet with the cut side facing up. Spread the cut surfaces with the spice mixture.
Grill the sweet potatoes under a preheated hot grill for about 5 minutes until they begin to brown.
Mix the dressing with the spinach and scatter over the Parmesan. Serve with the sweet potatoes.