Mix the butter, parsley, chives, garlic, lemon peel and seasoning in a bowl. Roll into four sausages and freeze. With a sharp knife, slice the chicken breasts almost in half horizontally so as to form a pocket. Open them up, lay over some clingfilm or parchment, and flatten them with a mallet or rolling pin. Set aside until the butter is nearly frozen.
Preheat the oven to Gas Mark 6, 200°C, fan 180°C.
Lay the breasts out open. Place one of the rolls of frozen butter down the middle of each then fold over the breast and secure as tightly with cocktail sticks. Carefully roll each breast in the seasoned flour, making sure it is well covered. Then roll it in the beaten egg and then in the breadcrumbs. Roll for a second time in the egg and a second time in the breadcrumbs.
Place the chicken breasts on a rack in the oven and cook for 40 minutes until the chicken is cooked through.