Heat the oil on a large skillet and fry the mushrooms for about 3 min. Add onions to the pan and cook together until golden brown. Fry the spinach in the olive oil and then cut it down. Mix the onions, mushrooms and spinach together in a bowl along with the garlic and breadcrumbs. Add salt and pepper to taste.
Mix all the spices together. Lay the chicken breast on a oven proof dish, season with the spice mix and cook in 180°C hot oven for 20-25 minutes, until the chicken breast has reached 73°C core temperature.