Slicing the cauliflower into steaks from the middle helps the head stay intact as you cut.
- 6 tablespoons vegetable oil, divided, plus more for grill
- 1 bunch scallions, trimmed
- Kosher salt, freshly ground pepper
- 1 1-inch piece ginger, peeled, grated
- ½ cup (packed) fresh cilantro leaves
- 2 tablespoons fresh lime juice
- Gochugaru (Korean red pepper powder), toasted black sesame seeds, and sesame oil (for serving)
Remove leaves and trim stem of cauliflower, leaving core intact. Place cauliflower, core side down, on a work surface. Starting at the midline of the cauliflower, slice from top to bottom into four ½" "steaks" (reserve any florets that break loose).
Prepare a grill for medium-high heat and lightly oil grate. Drizzle cauliflower steaks, florets, and scallions with 4 Tbsp. oil; season with salt and pepper. Grill scallions, turning occasionally, until charred in spots, about 2 minutes. Grill cauliflower steaks until tender and charred in spots, 8–10 minutes per side. Grill any loose florets in a grill basket, tossing often, until cooked through, 5–7 minutes.
Blend ginger, garlic, cilantro, lime juice, and remaining 2 Tbsp. oil in a food processor, thinning with water if needed, until sauce is the consistency of yogurt; season with salt.
Arrange cauliflower and scallions on a platter. Sprinkle with gochugaru and sesame seeds and drizzle with sesame oil. Serve with cilantro sauce alongside.