Heat 3 tablespoons of olive oil in a large saucepan over medium-high heat. Stir in the onion and garlic then cook until the onion has turned golden brown; about 5 minutes.
Stir in the tomato paste, cumin, salt, pepper and a pinch of chilli powder. Cook and stir 2 minutes more until the spices are fragrant.
Stir in the chicken stock, lentils and carrot. Bring to a boil over high heat then reduce the heat to medium-low. Cover and simmer until the lentils are soft; about 30 minutes.
Pour half of the soup into a blender filling the jug no more than halfway full. Hold down the lid of the blender with a folded kitchen towel and carefully start the blender using a few quick pulses to get the soup moving before leaving it on to puree. Puree in batches until smooth and pour into a clean saucepan. Alternately you can use a stick blender and puree the soup right in the saucepan. Do not puree all of the soup, leave it a little chunky.
Stir in the lemon juice and coriander then season to taste with salt. Drizzle with olive oil and a sprinkle of chilli powder to serve.