Preheat the oven to 425°F (220°C) and line a baking sheet with parchment paper or foil if desired.
In a large bowl or directly on the baking sheet, combine the cauliflower florets, drained chickpeas, and sliced red onion.
Drizzle the olive oil over the vegetables and chickpeas, then sprinkle on the garam masala, curry powder, smoked paprika, turmeric, cinnamon, and kosher salt. Toss until everything is evenly coated and spread in a single layer on the sheet.
Roast for 20–25 minutes, stirring or shaking the pan once halfway through, until the cauliflower is tender, chickpeas are crisped, and onion edges begin to brown.
While the vegetables roast, whisk together the plain yogurt, minced garlic, and lemon juice in a small bowl to make the garlic-yogurt sauce.
Warm the pitas if desired, then fill each pita with roasted cauliflower and chickpeas, drizzle with the garlic-yogurt sauce, and sprinkle with chopped parsley if using. Serve immediately.