Heat the oven to 400°.
Toss the carrots with 1 tbsp. oil and 1 tsp. salt and spread them over a rimmed baking sheet. Roast until they’re sweet and tender on the outside but still have a raw crunch in the center, 12 to 15 minutes. Let cool.
In a large salad bowl, combine the remaining 1⁄4 cup oil with the vinegar, harissa, sugar, spices, orange zest, and remaining 1⁄2 tsp. salt. No need to worry about emulsifying. Thinly slice the onion and toss it in the dressing, then pile in the carrots. Tear the mint leaves over the salad just before serving.
*Harissa, a North African chili-and-spice paste, can be found in well-stocked grocery stores and online.