In a saucepan, bring water to boil and dissolve stock cube.
Remove from heat but keep the stock hot.
Heat medium pot on medium-high heat, and add 2 tbsp cooking oil.
Saute onion for a minute then add garlic to cook for 30 seconds.
Add risotto rice to cook for 2 minutes, stirring frequently.
Add about 1/4 cup of hot stock, and stir until all the liquid is absorbed by the rice.
Continue adding stock about 1/2 a cup at a time, stirring frequently to release the starch.
Allow liquid to absorb before adding the next ladle of stock.
Continue stirring and cooking until you are left with the last 1/2 cup of stock.
Season with fish sauce to taste, and sugar.
Add prawn, stock, and frozen peas.
Then continue stirring until rice in al dente and prawn is cooked through.
Serve immediately with wedges of lime, and garnished with coriander leaves.