Heat 5 tablespoons oil in a wok over medium-high heat. Add prawns; saute until pink, about 3 minutes. Transfer to a plate.
Pour remaining 2 tablespoons oil into the wok. Add spring onions and ginger; cook and stir until fragrant, about 2 minutes. Return prawns to the wok; cook and stir for 1 minute. Add chicken stock, sugar, rice wine, soy sauce, bouillon granules, and salt; bring sauce to a boil. Reduce heat to low; simmer until flavors combine, about 2 minutes.
Arrange prawns on a serving plate; pour sauce on top.