Preheat the oven to 425°F and line a large baking sheet with parchment paper.
Cut the cauliflower into evenly sized florets and pat them dry.
Mix olive oil, harissa paste, honey, smoked paprika, cumin, garlic powder, salt, and black pepper.
Add the cauliflower and toss until thoroughly coated.
Spread the cauliflower in a single layer on the baking sheet.
Roast for 25 to 30 minutes, turning halfway through, until browned and tender.
Whisk tahini and lemon juice together, then gradually add water until smooth and creamy.
Transfer the roasted cauliflower to a serving dish and drizzle with tahini sauce.
Top with pomegranate arils, fresh herbs, and sesame seeds.
Serve warm.