1. Preheat oven to 400°.
2. Heat a medium saucepan over medium-high heat. Add 1 tablespoon olive oil to pan; swirl to coat. Add 1/2 cup onion and minced garlic; sauté 5 minutes or until golden. Add stock, lentils, and 2 teaspoons Cajun seasoning; bring to a boil. Cover, reduce heat, and simmer for 45 minutes or until lentils are tender.
3. Combine carrots, 2 tablespoons oil, and remaining 2 tablespoons Cajun seasoning, tossing well to coat. Arrange carrot mixture in a single layer on a baking sheet. Bake at 400° for 30 minutes or until tender.
4. Combine remaining 1 cup onion, remaining oil, cilantro, and remaining ingredients in a blender; process until smooth.
5. Place lentils on a serving dish; arrange carrots on top. Serve with harissa.