Mix the ingredients for the spiced oil together in a small bowl.
Prepare the grill for indirect cooking over medium-high heat (400° to 450°F). Preheat the sear grate over indirect medium-high heat for at least 10 minutes.
Stand the cauliflower on a cutting board. Cut from the top through the base in slices about 3/4 inch thick. Brush the cauliflower on all sides with the oil. Using the tip of a paring knife, make a few small incisions in the center of the core to ensure even cooking.
Carefully arrange the cauliflower slices on the sear grate. Close the lid and grill over indirect medium-high heat until the cauliflower is well marked and tender when pierced with a knife, about 25 minutes, turning once.
Transfer the cauliflower to a serving platter, brush with additional oil and lightly season with salt. Garnish with the cilantro and chile pepper.