Place chickpeas in a large container and cover with cool water; let soak 8 hours to overnight. Drain.
Bring 500ml of water to the boil in a large pot. Add chickpeas; reduce heat and simmer until almost tender, about 45 minutes. Drain and rinse with cold water until cool.
Spread chickpeas on a baking tray and remove skins.
Heat olive oil in a large pot over medium heat; cook and stir onion until softened, about 3 minutes. Add celery, carrots, garlic and fennel seeds; cook and stir for 4 minutes. Stir in chickpeas, vegetable stock and tomatoes. Simmer soup until chickpeas are tender, about 15 minutes. Add cherry tomatoes and spinach leaves; cook for 2 minutes.
Season soup with parsley, oregano, thyme, salt and pepper. Stir well and remove from heat. Cover and let stand for 10 minutes before serving.