I usually use dried chickpeas and cook them in the pressure cooker for 20 minutes. But its such a comforting dish, when I am short in time, I do use tins of chickpeas, which I always have in the cupboard.
The original Cretan recipe ask for 150ml of good extra virgin olive oil, which makes the soup velvety smooth. Cretans have the lowest heart disease rate in the world, which scientists put down to lots of fruit and veg, plenty of pulses and good extra virgin olive oil! Look it up, its true. I have reduced the olive oil for our western diet reasons and still find the soup delicious. Try both ways, you will taste the difference, but no decrease in the quality.