Scrub the potatoes clean, then cook in a large pan of boiling salted water for 20 to 25 minutes, or until tender but still holding their shape. Drain and set aside until just cool enough to handle, then slice into rough chunks, flaking away the skin as you go.
Place into a large bowl with the lemon juice and a good lug of extra virgin olive oil. Season lightly, then toss well so the potatoes absorb all those lovely flavours. Season to taste, then leave to cool completely.
Heat 1 tablespoon of olive oil in a small frying pan over a medium heat. Crush the olives with the flat side of your knife, tear out and discard the stones, then roughly chop the flesh. Add the olives and capers to the pan and fry for 2 to 3 minutes, or until crisp. Meanwhile, pick and roughly chop the coriander leaves, then trim and finely slice the spring onions. Stir them through the salad, sprinkle over the olives and capers, then serve.