Slice the top and bottom off the oranges. Run a sharp knife down each side to remove the peel and pith. Slice out each out each segment of the orange, saving the juice and removing any pips as you go.
Heat up the oil in a frying pan.
Pat the chicken dry if necessary, season with salt and pepper, then carefully pop in the hot oil. Leave for a couple of minutes to let the chicken start to colour underneath.
Give a stir and cook until the chicken has cooked through. Splash in the orange juice and balsamic vinegar and let the sauce reduce, sweeten and become syrupy.
Layer up the watercress, orange segments and chicken and enjoy.