Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Cut the chicken breast into bite-sized pieces and place them on one side of the baking sheet.
Add the broccoli florets, cauliflower florets, and rinsed chickpeas to the other side of the baking sheet.
Drizzle the olive oil over the chicken, vegetables, and chickpeas, then sprinkle evenly with sea salt, black pepper, and garlic powder.
Toss everything gently to coat and roast in the oven for 18 to 20 minutes until the chicken is cooked through and the vegetables are tender.
While roasting, whisk together the tahini, lemon juice, and water in a small bowl until the dressing is creamy and smooth.
Place the cooked quinoa in the base of a bowl and top with the roasted chicken, vegetables, and chickpeas.
Drizzle the lemon-tahini sauce over the top and serve immediately.