750 g piece salt cod (bacalhau)750 g potatoes, peeled125 ml (½ cup) extra-virgin olive oil4 cloves of garlic, thinly sliced2 x 400 g canned chickpeas, drained and rinsed1 small red onion, halved and very finely sliced60 ml (¼ cup) sherry vinegar, or to taste4 hard boiled eggs, peeled and cut into wedges(½ cup) pitted black oliveswatercress, chopped coriander and sweet paprika, to serve