Preheat oven to 425 degrees and line a baking sheet with parchment paper. In a large bowl, add the sweet potato, cauliflower, and chickpeas, then drizzle with 1 tablespoon of the olive oil and sprinkle in the za'atar seasoning and salt. Toss gently to coat and turn out onto the baking sheet, creating a single layer. Roast for 30 minutes, or until the vegetables are tender and browned. Remove from oven.