Heat the oven to 200C/fan 180C/gas 6. Tip a couple of tbsp olive oil into a small roasting tin. Add the lemon slices and then sit the chicken on top. Rub the top of each chicken breast with a little olive oil and then season well. Squeeze over the juice from the remaining lemon half and put the thyme sprigs between the chicken breasts.
Roast for 20-25 mins until the chicken is cooked through – check by poking a knife into the centre of each breast to make sure the juices run clear. Rest for 5 mins before serving.