Preheat oven to 400°F and line a large baking sheet with parchment paper.
Cut the chicken breast into bite-sized cubes and place them on one side of the baking sheet.
Add the cauliflower florets, broccoli florets, and rinsed chickpeas to the other side of the sheet.
Drizzle the chicken and vegetables with olive oil and season evenly with sea salt, black pepper, garlic powder, and smoked paprika.
Toss everything to coat well, then spread into a single layer.
Roast for 20-25 minutes until the chicken is cooked through and the vegetables are tender with slightly charred edges.
While roasting, whisk together the tahini, lemon juice, and water in a small bowl until the dressing is smooth and creamy.
Assemble the bowl by layering the roasted vegetables, chickpeas, and chicken, then finish with a generous drizzle of the tahini dressing.