In a small bowl, mix together the chili, paprika, cayenne, garlic, mustard, salt, pepper, and onion salt. Set aside.
Remove the leaves from the bottom of the cauliflower. Cut each head in half right down the middle, then cut a thick 1 ¼” slice on one side of the cauliflower half, and then another thick 1 ¼” slice on the other side of the cauliflower half. Be careful to keep the stem intact so that you can get a thick “steak” rather than a bunch of florets.
Preheat a grill to medium high on one side, and brush the cauliflower steaks with olive oil. Sprinkle with the buffalo seasoning on all sides. Grill on direct heat (over the flames), lid closed, on each side for about 6 to 9 minutes, or until tender-crisp when poked with a fork and lightly charred. If you find your cauliflower is charring faster than it is cooking through, transfer to the indirect heat, and cover with the lid to finish cooking through. Once tender-crisp, transfer to a baking sheet and glaze generously on both sides with the glaze.
Return to the grill over direct heat for one minute per side, or until the glaze just
To serve, top with cauliflower with the crumbled blue cheese, ranch (if using) and chives.