Put the beans in a bowl with plenty of cold water and let soak overnight. Drain, transfer to a saucepan and cover with fresh water. Bring to a boil rapidly for 10 minutes.
Reduce the heat and add the thyme, bay leaves and onion. Simmer very gently for about 1 hour until tender. Drain and discard the herbs and onion.
Mix together the garlic, cumin, scallions, parsley, lemon juice and oil. Season with salt and pepper. Pour over the beans and toss lightly together. Gently stir in the eggs and cucumber and serve at once.