Start by removing the green leaves from the cauliflower head. Cut off the stem a little if needed, so it can be placed flat on a surface. Mix the sumac and curry in a small bowl and stir well. Brush a thin layer of oil evenly all over the cauliflower head. Now sprinkle an even layer of the spice mix on the cauliflower.
Light the grill and prepare it for indirect grilling, aim for 175° C / 350° F. Place the cauliflower head on the indirect side, add 1-2 wood chunks for smoke flavor, and close the lid. Check doneness by poking it with a sharp knife. The thick stem should be al dente, the smaller bouquettes a little softer. Time may vary a little here depending on cook temp.
Mix the ingredients for the dip sauce as soon as the cauliflower is on the grill. Use more or less honey if you wish, but let it sit in the fridge while the cauliflower is on the grill, this way the flavors have time to blend.