Place chicken in a small bowl. Add spice, 1/2 tsp salt and 3 tsp oil, and massage into the chicken on both sides. Set aside to marinade.
Place the potatoes in a medium-sized pot filled with enough cold water to cover the tops and 2 tsp salt. Bring to a boil. Reduce to rolling simmer and cook for 15 minutes.
In the meantime, heat a generous glug of oil in a large cast-iron pan on medium heat. Fry onion and mushrooms, then add capsicum and parsley after about 10 minutes. Stir and continue to fry gently until all the ingredients are soft and browning. Add ¼ teaspoon of salt and spinach. Stir and cook a further 5 minutes. Transfer to a bowl and set aside.
Check the potatoes are nice and soft, drain, retaining some of the cooking liquid in the pot. Add butter, sour cream and ¼ teaspoon of salt. Mash with a potato masher until smooth.
Add more oil to the pan you used for the vegetables, sear chicken on one side and fry gently for approximately 10 minutes or until golden brown. Repeat on other side.
Push chicken aside and add mushroom mix to briefly reheat before serving. (Make sure not to skip this step as the mix will deglaze the pan and flavour the vegetables).
