Preheat the oven to 400°F. On a baking sheet, toss the cauliflower and chickpeas with olive oil, cumin, chili powder, garlic powder, salt, and pepper. Spread in an even layer and roast for 25-30 minutes, or until the cauliflower is tender and golden.
In a small bowl, whisk together tahini, lemon juice, minced garlic, and water. Start with 2 Tbsp. of water and add more as needed to achieve a creamy, pourable consistency. Season with salt and pepper to taste. Heat the gluten-free tortillas according to package instructions until they are soft and pliable.
Lay out the tortillas on a clean surface. On each tortilla, layer the mixed greens, a portion of the roasted cauliflower and chickpeas, and sliced red onion. Drizzle with the tahini dressing and add any optional toppings. Carefully roll up the tortillas, folding in the sides to enclose the filling. Serve immediately, with extra tahini dressing on the side for dipping if desired.