Peel and dice the root vegetable, put them in a pan of lightly salted water and bring to a boil. Gently simmer for 15 minutes, until tender. Drain, add some butter/spread, season with salt & pepper, then mash with a potato masher. Mix in the fresh herbs and set aside.
Meanwhile slice the onion and garlic. Cut the chicken and mushroom into chunks.
Heat a couple of spoonfuls of olive oil in a frying pan and gently soften the onion and garlic. Add the herbs, chicken and mushroom, then stir-fry for 3-5 minutes. When the chicken is cooked (or warmed) through, add the spinach and the cayenne, if used. Add a few squeezes of lemon. Cover and cook for a minute or so.
When you’re ready to bake the pie, turn the oven on and set the temperature to 200°C.
Transfer the chicken and mushroom filling into a deep roasting dish, spreading it out evenly.
Spoon the mash on top, covering the chicken filling completely and evenly.
Sprinkle some grated cheese (if you like), season with black pepper and put the pie in the oven.
Bake for about 20-30 minutes, until the topping is crispy and/or the cheese is sizzling and brown.
Serve warm.