Heat oil in a large heavy based saucepan, add red onion and garlic and sauté gently for 1 minute then add risotto rice and toss for 2 minutes to coat the grains in oil.
Gradually add ½ a cup of stock at a time, stirring until liquid is absorbed before adding more.
Cook for 12-15 minutes until the risotto rice is just al dente.
Stir in prawns, asparagus and snow peas and cook and 2-3 minutes until prawns are pink and plump then lastly stir through mascarpone, dill, lemon zest and season well.
Garnish with whole cooked prawns and lemon wedge if desired. Serves 4.