Heat the oil in a large pot over medium low heat. Add the onions and minced garlic and cook for a few minutes until the onions are fragrant and softened.
Add the chicken and cook for 2-3 minutes, browning it a little. Add curry powder and paste; cook for 3-5 minutes.
Add the coconut milk, and let simmer for 15-20 minutes or until the chicken is fully cooked.
Add water or chicken stock depending on the consistency you want for the sauce, or let simmer longer to thicken if needed.
Stir in the brown sugar, fish sauce, and lime juice. Taste and salt if needed
Top with fresh cilantro, serve over cooked rice.