Sprinkle both sides of the chicken with salt and pepper. Heat the oil over high heat, then add the chicken thighs, skin side down. Cook for about 5 minutes until the skin is nice and golden, then turn over and cook for another 3 minutes. Transfer the chicken to a plate and set aside.
Drain away most of the excess oil, leaving about 1 tablespoon in the pan. Turn the heat down to medium. Add the onion, celery and garlic and saute, stirring often for 2-3 minutes until starting to turn translucent.
While cooking the vegetables, in a small bowl, pour the boiling water over the dried porcini. Let it sit for about 2 minutes to soften, before scooping out the mushroom and finely chopping them.
Strain the porcini stock into the chicken stock to remove any grit. Add the Swiss brown mushrooms and saute for another minute, then add the orzo, and saute for another 2 minutes.
Now, add the salt, pepper, chopped porcini, and stock and give the whole lot good stir. Bring it to the boil then add back the chicken, skin side up. Turn the heat down to low, so you just have a very slight simmer. Cover and cook for around 10-12 minutes until the orzo is tender.
Scatter over the finely chopped parsley right before serving