Thinly slice 3 of the lemons, setting aside 8 large slices. Grate the rind and squeeze the juice from the fourth lemon, and set aside.
Using a sharp knife, make a pouch in the middle of each chicken breast. Fill each chicken pocket with the smaller slices of lemon, some chopped oregano leaves and salt and pepper.
Heat a griddle pan (or ordinary frying pan). Sandwich each chicken breast between 2 of the reserved large lemon slices and a sprig of oregano. Place the chicken in the pan and cook for 8–10 minutes on each side – try to keep the lemon intact with the chicken so that all the citrus flavour infuses into the chicken.
Meanwhile, bring a large saucepan of lightly salted water to the boil. When boiling, plunge the spaghetti into the water and cook for 12 minutes, or according to the instructions on the packet. Drain well, then toss with the lemon rind and juice, the parsley, the olive oil and seasoning to taste. Serve with the lemon chicken.