Blend the tomatoes, onion and garlic. Heat the oil in a heavy-based casserole, add the blended vegetables and cook gently for 10 minutes until the mixture has reduced. Pour in the water, allow to return to a simmer, then add the beans.
Simmer for 15 minutes, then add the lemon juice, herbs and spices. Season lightly with salt. Leave over a gentle heat for a further 5 minutes, then serve warm.