Preheat the oven: Set your oven to 400°F and let it heat up fully.
Dry the chickpeas: Spread the drained chickpeas on a clean dish towel or several layers of paper towels. Pat them dry thoroughly with another clean towel or paper towels to remove as much moisture as possible.
Prepare and roast the vegetables: In a large bowl, combine the sweet potatoes and carrots with 2 tablespoons of olive oil. Sprinkle them with ¾ teaspoon of kosher salt, black pepper to taste, and the thyme sprigs. Mix well, then spread the vegetables evenly on a large, rimmed baking sheet. Roast them in the oven, tossing occasionally, for 40–50 minutes, or until they become golden brown and tender.
Season and roast the chickpeas: While the vegetables are roasting, toss the chickpeas in a bowl with 2 tablespoons of olive oil, the chili powder, cumin, and a generous pinch of salt. Spread the chickpeas evenly onto a second rimmed baking sheet. Add the chickpeas to the oven about 10 minutes after the vegetables have started roasting and cook them for 30–40 minutes, or until they are crisp and golden. Once done, let both the vegetables and chickpeas cool slightly before assembling the salad.
Make the yogurt dressing: In a small bowl, whisk together the yogurt, lemon juice, garlic, and the remaining 4 tablespoons of olive oil until smooth and creamy. Taste and adjust the seasoning with salt and pepper as needed.
Combine the salad: In a large mixing bowl, add the spinach, roasted vegetables, roasted chickpeas, and shallots. Drizzle the prepared dressing over the mixture and gently toss everything together until the dressing evenly coats the ingredients. Serve immediately for the best flavor and texture.