Heat oven to 200C/180C fan/gas 6 and sit the chicken in a small roasting tin. Mix all the spices with 2 tsp salt using a pestle and mortar – try to grind the oregano finely so that it doesn’t burn. Rub the spice mix over the chicken with some oil, and cover loosely with foil.
Sit the potatoes in another tin, and put them in the oven together with the chicken. After 30 mins, remove the foil. Pierce the banana once in the skin with a knife and put alongside the potatoes, and roast with the chicken for another 30 mins.
Check the potatoes are soft, then remove them and the banana from the oven. Leave the chicken to cook for a final 10 mins. Split the potatoes and banana, and scrape all the flesh into a saucepan. Add 1 tsp salt, half the butter and the milk, then mash together. Season.
Check the chicken is cooked by piercing the inner thigh and ensuring the juices run clear. Lift to a serving platter and rest for 10 mins.
To serve, spoon the mash into a dish, topped with knobs of remaining butter, and carve the chicken at the table. Serve with Creamed corn & bacon (recipe in 'goes well with', right).