Place the chickpeas in a large bowl, cover with water and leave to soak overnight.
Drain and place in a large saucepan. Cover with water and bring to the boil, then simmer for 1 ¾ hours, or until tender.
Drain thoroughly.
Heat the oil in a heavy-based frying pan, add the onion and cook over low heat for 5 minutes, or until softened and just starting to brown.
Cut the tomatoes in half, remove seeds with a teaspoon and dice.
Add the tomato to the pan with the cinnamon and garlic, and cook for 2-3 minutes, or until softened.
Thoroughly wash the swiss chard and pat dry with paper towels. Trim the stems and finely shred the leaves.
Add to the tomato mixture to the chickpeas and cook for 3-4 minutes, or until the swiss chard wilts.
Add the mint, lemon juice and sumac, season, and cook for 1 minute. Serve immediately.