In a medium saucepan, warm sesame oil over low heat. Add the red Thai curry paste and cook, stirring constantly, for 5 minutes.
Meanwhile, bring 8 cups of water to a boil in a large saucepan. Add the wontons and cook for 3 minutes.
Remove the wontons from the water with a slotted spoon and place in warm bowls.
Add the sugar, fish sauce, and coconut milk to the medium saucepan. Cook on low heat for 4 minutes, stirring constantly. Season with the lime juice, salt, and pepper, while taking care not to bring to a boil.
Pour the soup over the wontons. Garnish with the cilantro and Thai chilies, and serve.