01 - Preheat the oven to 425°F (220°C). Line a large baking sheet with parchment paper.
02 - In a large mixing bowl, whisk together olive oil, turmeric, cumin, coriander, smoked paprika, salt, and black pepper until evenly blended.
03 - Add cauliflower florets and sliced red onion, if using, to the bowl. Toss thoroughly to evenly coat with the spiced oil mixture.
04 - Spread the coated vegetables in a single layer on the prepared baking sheet for even roasting.
05 - Roast in the preheated oven for 20 to 25 minutes, stirring once halfway through, until the cauliflower is golden brown and tender with crispy edges.
06 - Transfer the roasted vegetables to a serving platter. Garnish with chopped cilantro or parsley and serve with lemon wedges.