In a small bowl combine turmeric, cumin, paprika, mustard powder, cayenne or chili flakes if using, salt, and black pepper. Stir to thoroughly combine.
Sprinkle spice mixture over cauliflower and toss again until spices are well distributed. Spread out in a single layer flat side of each floret down, with as much space between cauliflower florets as possible so that they caramelize nicely.