Put a large saucepan of water with a pinch of salt on to boil for the potato. Peel the potato and chop into 2cm chunks. When the water is boiling, add the potato to your pan and cook, 15-20 mins. Meanwhile, halve the tomatoes and roughly chop the parsley (stalks and all). Pot the tomatoes in a bowl, squeeze on some lemon juice and mix in half the parsley. Season with salt and pepper. Trim the tops from the green beans.