Spray a large pan with low-calorie cooking spray and place over medium heat.
Sauté the onion for 5 minutes until soft. Add garlic and ginger, and cook for another 2–3 minutes.
Add the chicken and brown on all sides. Stir in the cumin, coriander, smoked paprika, and chilli flakes. Cook for 1–2 minutes to release the flavours.
Stir in the chopped tomatoes, tomato purée, sweet potato, and chicken stock. Bring to the boil, then reduce the heat and simmer for 20 minutes, stirring occasionally.
In a small bowl, mix the peanut butter with a few spoonfuls of the hot liquid from the stew until smooth. Then stir the mixture back into the stew.
Simmer for another 10 minutes, or until the sweet potatoes are tender and the sauce has thickened.
Squeeze in the lime juice, season with salt and pepper to taste.