Cut the chicken thighs into thin strips and place them in a resealable bag along with the onion. Add in all of the remaining chicken marinade ingredients and squish it with your hands to ensure that the chicken is evenly coated in the marinade. Place in the fridge for 4 hours but ideally overnight.
Preheat the oven to 200 degrees Celsius (400 Fahrenheit) and empty the contents of the marinating chicken bag out onto a large baking tray. Use a fork to ensure everything is spread out evenly and then bake in the oven for 30 minutes until all of the chicken is cooked.
While the chicken is cooking, in a blender or nutribullet container combine all of the ingredients for the tahini sauce and blend until completely smooth. The consistency should be fluffy.
To assemble the platter spoon 1/2 the tahini sauce down onto the centre of the plate and arrange the watercress around the outside. Place all of the chicken down onto the place on top of the tahini sauce. Garnish by drizzling the remaining tahini sauce over the chicken and watercress and place the slices of radishes overtop, along with the pomegranate seeds and chopped parsley.