Heat oil in a large saucepan and saute onion and carrots over low heat until light golden, about 5 min. Stir in paprika, cumin seeds, tomato powder (or paste), red pepper flakes and salt. Cover and cook for another 5 to 7 min. Add lentils and stir everything together so tomato, spices and lentils are thoroughly combined. Add broth (or water), cover and cook until everything is very tender, about 30 to 40 min. (Or use a pressure cooker and cook until very tender.) Use an immersion blender or stand blender to puree the soup into a smooth consistency. (Skip this step if you prefer a chunky soup.) Crumble the mint leaves into the soup. Stir and simmer for 2 to 3 more min. Remove from heat and stir in half of the sumac, saving the rest for garnish. Ladle soup into bowls and serve with lemon wedges and/or a squeeze of lemon juice, fresh mint, plus a generous sprinkle of sumac.