Remove the cooked lobster from its shell. Remove the meat by taking the claws out of the shell and striking them with the back of a knife. Separate the head from the tail, place the tail on a flat surface, cut the skin lengthwise with kitchen scissors and scoop out the flesh. Rinse the lobster meat in cold water, cover and refrigerate. Slice the carcass coarsely and rinse in cold water to drain the water.
Clean the soup herbs and chop coarsely. Heat 3 tablespoons of oil in a high pot and fry on medium heat for 5 minutes on all sides. Add vegetables and cook for another 5 minutes. Deglaze with cognac, fill with 2.5 liters of water, add salt and pepper and cook in an uncovered pan over medium heat for 50 minutes. Remove turbidity from the surface. Add bay leaves and thyme 10 minutes before the end of cooking time. Pour the broth through a cloth into a bowl and set aside (approximately 1.5 liters).
In the meantime, lightly fry the coriander seeds in a pan without oil, and then grind them finely in a mortar. Peel the potatoes, cut them into 1/2cm pieces, and soak them in cold water. Peel the carrots and cut into 1/2 cm cubes. Wash celery, remove threads and cut into 1/2 cm cubes. Peel the onion and chop finely. Wash the green onion and cut the white part and the light green part in half lengthwise, and then slice diagonally into 1/2cm thick. Wash the chili peppers, cut in half lengthwise, remove the seeds, and chop finely. Boil lentils in water for 5 minutes and drain.
Heat 3 tablespoons of cooking oil in a saucepan and fry the onion over medium heat for 2 minutes without color. Add the lentils and fry for another 3 minutes. Pour in the stock and cook for 45 minutes, uncovered, stirring occasionally. 10 minutes before the end of cooking time, add potatoes, carrots, celery, chili and coriander seeds. Add green onions 2 minutes before the end of cooking time. Cut the lobster claws in half or 1/3 depending on the size. Cut the lobster tails crosswise.
Heat the remaining oil in a large frying pan and fry the lobster meat for 3-4 minutes over medium heat, then season with salt and pepper. Sprinkle coriander over the soup and serve with lobster meat.