Put the stock into a large saucepan with the ginger peel and boil for 15 minutes. Set aside and allow to steep for a further 15 minutes.
Strain the stock into a clean saucepan. Add the soy sauce, strips of ginger, spring onions, broccoli and chilli, if using, and simmer for 5 minutes.
Add the scallops, simmer for a further 3 minutes, or until the scallops are just cooked through. Season with Thai fish sauce and lime juice.
Remove the scallops from the soup with a slotted spoon and put 3 in each individual soup bowl. Divide the broccoli among the bowls and pour in the hot soup. Serve immediately with a few drops of sesame oil.