Cut the head of cauliflower into small, bite sized florets. Place the florets in a large bowl and add the oil, cumin, turmeric, salt and pepper, then toss to coat.
Spread the cauliflower onto a baking sheet and roast, stirring once halfway through, until tender and browned in spots, 20 minutes.
While the cauliflower is roasting, make the salad base. In a large bowl, combine the arugula, parsley, red onion, sesame seeds, and black olives. Toss to combine, then spread the salad onto a platter.
Make the dressing. In a small bowl, whisk the yogurt, olive oil, tahini, lemon juice and pepper in a small bowl. Thin with water to achieve desired consistency. Taste for seasoning and add additional pepper if needed (skip the salt, as the olives add a briny kick).
Top the salad with the roasted cauliflower, then drizzle with the yogurt tahini dressing. Serve warm or at room temperature.
The roasted cauliflower keeps well on its own in the fridge in a sealed container. Reheat by sauteing in a dry pan over high heat or in the microwave for 1 minute. Alternatively, serve it cold as a packed lunch with the salad base.