Preheat oven to 450°.
Whisk garlic, oil, maple syrup, Harissa, and cumin seeds in a large bowl; season with salt and pepper.
Add carrots and lemon to the bowl and toss to coat them with the maple syrup/Harissa mixture. Spread carrots in a single layer on a large roasting pan: season with salt and pepper.
Roast, tossing occasionally, until carrots are fork tender and lemons are caramelized, about 35–40 minutes.
Before serving, sprinkle carrots with finely chopped fresh parsley. Serve the carrots straight from the oven, or room temperature.