Bring a large saucepan of salted water to the boil and drop in your green beans. Cook for 4 minutes or until just soft and cooked through. Lift them out with a slotted spoon and drain.
Add the pasta to the water and cook according to packet instructions. Serve it al dente, like they do in Italy – this means the pasta is just cooked, but still has a little bite. Drain in a colander and rinse under cold water until cool.
Put the olives on a chopping board and squash them with the bottom of a mug so the stones pop out. Throw the stones away and lightly chop the olives.
Squeeze the lemon juice into a big mixing bowl and add three times the amount of olive oil. Season with salt and pepper. Drop the cooked beans, pasta, olives, mackerel and halved tomatoes into the dressing and toss until everything's mixed together. Serve the salad on four plates, sprinkled with parsley leaves.
Tip: Always buy olives with stones and take them out yourself. They taste much better than pitted ones.