Trim the green beans, then add to a pan of boiling salted water over a medium heat and cook for 4 minutes, or until tender. Remove the beans from the water with a slotted spoon, and drain. Add the pasta to the water and cook according to the packet instructions, then drain and rinse under cold water until cool. Destone and finely chop the olives. Halve the tomatoes, then drain and break the mackerel into pieces. Squeeze the lemon juice into a large bowl, add three times the amount of oil, then season with sea salt and black pepper. Drop the beans, pasta, olives, mackerel and tomatoes into the dressing, then toss together. Pick over the parsley leaves, to finish.