Heat a skillet over medium heat. Toast coconut 2 to 3 minutes, stirring frequently. Remove to a plate. Add remaining 1 tsp oil to skillet. Add garlic and ginger to skillet; sauté 1 minute. Pour in coconut milk, lime juice, fish sauce, remaining 1 tbsp brown sugar, remaining 1/4 tsp salt and remaining 1/8 tsp cayenne. Bring to a simmer. Mix cornstarch with 1 tsp cold water. Add to mixture and simmer 2 minutes, until thickened.