Preheat your oven to 400°F (200°C).
Transfer the carrots to a bowl. Add olive oil, sumac, cinnamon, honey or maple syrup, salt, and pepper to taste.
Toss to combine, then transfer the carrots to the lined baking tray in a single layer.
Roast for 25-30 minutes, tossing mid-cooking (see notes). Check for doneness by inserting a fork in the thickest part of the carrot. It should go in easily.
Meanwhile, bring a large pot of salted water to a boil. Cook the buckwheat according to package instructions. Once done, drain, then set aside in a bowl.
Remove the carrots from the oven, then taste and adjust the seasonings.
Whisk all the dressing ingredients together in a small bowl.
Add the diced cucumber, red onion, tomatoes, and parsley to the cooked buckwheat. Toss to combine.
Pour the dressing over the buckwheat mixture and toss until everything is well combined. Taste and adjust the seasoning if needed.
Transfer the buckwheat tabbouleh to a serving dish, top with the roasted carrots, and serve.