Heat the olive oil in a large pot over medium heat. Add the onions, carrots and celery and sauté for about 15 minutes, stirring now and then. The longer they go, the more flavor they give the soup.
Add the garlic, tomato paste, oregano, coriander, turmeric, red pepper flakes and curry. Stir for 1 to 2 minutes so the tomato paste and spices wake up.
Add one can of drained chickpeas (whole) and the vegetable broth. Bring to a boil, then lower the heat and simmer for 20 minutes.
While the soup cooks, make the puree: in a food processor, blend the second can of drained chickpeas with the tahini, the lemon zest, all the lemon juice, and about 1/2 cup of the broth until smooth.
Stir the puree into the soup and let it simmer a few minutes, until the broth looks creamy.
Add the cubed potatoes last and cook for about 15 minutes, until the potatoes are tender.
Take the pot off the heat. Stir in the finely chopped dill and parsley. Taste and add salt and pepper — go easy at first if your broth is already salted, or use sodium-free broth and salt it yourself.
Serve with extra dill and parsley on top of each bowl.