Put 500ml of the chicken stock into a pan. Add the lentils and simmer until tender, about 20 minutes. Heat 1 tbsp olive oil in a non-stick frying pan.
Put the chicken breasts in skin-side down and cook until the skin is golden brown. Turn over and cook for 5-6 minutes add the garlic to the pan, stir for a minute, then add the rest of the stock, lemon juice and zest and simmer for a couple of minutes.
Drain the lentils and toss through the parsley. Slice the chicken and serve on a bed of lentils with the pan juices spooned over.