Tahini, a sesame paste, is popular in Middle Eastern cooking. Find it in the supermarket in the international section, or with the peanut butter. Stone-ground mustard contains whole mustard seeds, and adds texture and flavor. Make the sauce a few hours ahead and refrigerate it.
Preheat the oven to 400 degrees. Put the carrots in a large bowl and toss with the olive oil, garlic powder, cumin, cinnamon and salt. Spread the carrots onto a baking sheet and roast for 15–20 minutes, or until a sharp knife slides in easily.
In a small bowl, whisk together the tahini, honey, lemon juice and mustard.
Spread the tahini sauce onto a serving platter or individual plates. Place the carrots on top, and garnish with chopped chives, if desired.