Thinly slice the onion.
Heat the oil in a casserole dish and gently sauté the onion for five minute. Add the chicken and cook for 10 minutes until lightly browned. Keep turning them over.
Meanwhile slice the pepper and dice the sweet potatoes. Add these to the chicken and cook for a further 5 minutes, under cover.
Mix the hot chicken stock with the harissa paste and sun-dried tomatoes and pour over the chicken.
Bring to the boil, cover and gently simmer for 35-45 minutes until the chicken is cooked through and the sweet potatoes are tender.
Add the spinach, cover and cook for a couple of minutes until the leaves have wilted.
Serve warm.