Heat oil in a large dutch oven over medium heat.
Add chopped onions and shallot and cook until fragrant and softened.
Stir in garlic, harissa paste, curry powder, turmeric and coriander and cook for about 2 minutes.
Add carrots, stir and cook for a few minutes.
Add lentils, vegetable broth and salt. Stir and bring to a boil. Cover and reduce heat to a gentle simmer. Cook until carrots are tender, about 30 minutes.
Add tahini and stir to combine.
Using a hand blender, blend the soup until smooth. If the soup is too thick, add ½ cup water.
Stir in lemon juice.
Serve with herbs, pumpkin seeds and crispy croutons.