Heat the oil over medium in a 4 to 5 quart soup pot or Dutch oven until the surface shimmers. Add the onions and sweat, stirring frequently, for about 5 minutes or until softened.

Spoon in the Thai red curry paste, ginger, and lemongrass (if using), along with the garlic. Stir into the onions and let cook for a minute or two, until the mixture is fragrant.

Increase the heat to medium-high, and pour in the chicken broth and coconut milk. Bring the soup to a low boil, then adjust the heat to maintain an active simmer.

Stir in the fish sauce and sugar, then add the dumplings. Let the soup come back up to bubbling, and cook for the time indicated on the packaging to ensure they’re properly heated through.

Turn off the heat and add the spinach, green onions, and cilantro. Let the soup stand until the spinach wilts. Squeeze the juice from half of the lime into the soup and stir. Taste, and squeeze the other half if it needs it.

Ladle into bowls and add your favorite toppings.