Preheat your oven to 400°F. Cut the top part of a garlic head and drizzle it with 1 tablespoon of olive oil. Wrap it tightly in aluminum foil and set aside.
Place the carrots and onion quarters on a baking sheet. Drizzle with olive oil, and season with turmeric, paprika, cumin, coriander, salt, and black pepper. Mix everything well to ensure the vegetables are well-coated. Add the wrapped garlic to the baking sheet.
Place the baking sheet in the oven and roast for about 40 minutes, or until the carrots are tender and the vegetables have caramelized edges.
Remove the baking sheet from the oven and place the vegetables in a pot over medium heat. Unwrap the garlic and squeeze it into the pot as well. Add in the broth.
Heat the soup over medium heat and let it simmer for about 10 minutes. Then blend the soup using an immersion blender. Alternatively, you can blend it in a regular blender, but make sure to do it in batches.
Add in the lemon juice and adjust seasoning if needed. Cook the soup for 10 more minutes.
Serve hot, garnished with fresh parsley and a sprinkle of Aleppo pepper if desired.