Heat the oil in a large skillet over medium heat. Add cumin, chopped onion, and cook until the onion has softened and turned translucent, 3 to 4 minutes.
Stir together tomato paste and water, and pour into skillet. Stir in chicken, and cook until it has firmed and turned white, about 5 minutes. Add coconut milk, brown sugar, cayenne pepper, turmeric, salt, and pepper. (if using dried cilantro, add it in now).
Bring mixture to a simmer, then reduce heat to medium-low, cover, and continue to simmer until the chicken is done, about 15 minutes. If using fresh cilantro, sprinkle it on before serving.