Heat oil in a single-serving small pot over medium heat.
Add garlic and onion; sauté until fragrant and softened.
Stir in the red curry paste and cook for 30–60 seconds to release the flavor.
Pour in the chicken broth, fish sauce, and sugar. Stir to combine.
Add milk or coconut milk, then bring the soup to a gentle simmer.
Drop in the frozen soup dumplings. Cover and cook for 10–12 minutes, until dumplings are heated through.
Squeeze in lime juice.
Uncover, drizzle with chili oil if desired, and garnish with green onions. Serve hot.