If you are using bamboo skewers, soak them in water before you get started.
Trim up the duck breast and cut each of them into 9 equally sized chunks.
Top and tail the red onion, peel it, then cut it into 6 wedges. Remove the centre of the onion, and cut each of the wedges in half widthways.
Heat a small (15cm or 6") saucepan over a medium heat and add the marmalade, orange juice, red wine vinegar and nutmeg, then cook until the marmalade "melts" and a glaze forms.
Heat your grill (broiler) as high as it will go.
Thread the duck and onion onto 6 skewers. I start with duck, then red onion, then duck, red onion and a final piece of duck. You need to keep the skin of the duck all on the same side of the kabob, then season them with salt.
Brush the kebabs with the marmalade glaze and slide them under the grill, skin side up, and cook for 3-4 minutes until the fat starts to render and you get a nice dark caramelisation on the duck skin.
Rotate the kebabs 120°, brush with more of the glaze and cook for another couple of minutes.
Rotate another 120° brush again and cook for a final couple of minutes.
Remove from the grill and rest for 3-4 minutes, then finish by brushing them with any leftover glaze.