In a bowl, combine cinnamon, black pepper, cumin, paprika,garlic powder and salt.
Rub the spice mix all over the chicken thighs to coat evenly.
Heat a little oil in a large pot over medium-high heat.
Place the seasoned chicken thighs skin-side down and sear for about 3–4 minutes per side until golden brown.
Remove chicken and set aside.
In the same pot, add sliced onion, potatoes, sweet pepper, and garlic (if using).
Stir and sauté for 3–5 minutes until slightly softened and coated with the chicken flavors. Return the chicken to the pot with the vegetables.
In a small bowl, mix the tomato paste with hot water until smooth. Pour over the vegetables and chiken, cover the pot, and let it simmer for 15 minutes.
Transfer the vegetables into a baking dish (casserole dish).
Place the chicken thighs on top of the vegetables.
Cover the casserole dish with foil.
Bake in a preheated oven at 200°C (400°F) for 35 minutes, or until the chicken is fully cooked (juices run clear) and the potatoes are tender.
In the last 10 minutes, remove the foil to allow the chicken skin to crisp.
Garnish with chopped parsley or green onions.
Serve hot with rice, bread, or a fresh salad.