Combine the smoked paprika, garlic powder, cumin, chili powder, five spice powder, dry mustard and some salt and pepper in a bowl. Using a sharp knife, score the skin of the duck so it has a 1/4-inch diamond pattern. Rub the spice mixture all over the duck.
Heat a grill to medium (make sure it's not too hot since the key is to cook duck slowly to render the fat) and wipe down the grates with an oiled towel. Place the duck skin-side down on the grate and cook until the skin is seared and the fat is rendered, 4 to 5 minutes. (If there are occasional flare-ups from the fat, move the duck around on the grill to a new spot away from the flame each time.) Flip the duck over and place on a cooler part of the grill. Cook for an additional 5 minutes for medium-rare. Let rest for 5 to 7 minutes before cutting against the grain into thick slices.