In a frying pan, add in some oil and fry the prawns for about 2 minutes on each side until cooked.
Set aside, then fry the mushroom slices for about 2 mins on each side until golden. Remove and set aside.
Next, add a touch more oil, and fry the diced shallots and lemongrass until softened.
Then add tomatoes, and cook these down for about 10 minutes until they have burst, then deglaze with water (about 100ml).
Add galangal or ginger, kaffir lime, and chillies and leave to infuse on a low heat for about 5 minutes.
Add the thai chilli paste, fish sauce, maple syrup and half the lime juice, followed by the coconut milk.
Mix well and leave to simmer on a low heat.
In the meantime, cook the orzo in salted water until very al dente.
Remove the pieces of galangal or ginger and lime leaves from the tom yum sauce, and then drain the orzo and add this to the sauce.
Mix well to combine. At this point season to taste with more salt and sugar where needed.
Serve the orzo in a bowl and top with the cooked prawns, the juice of half a lime, mushrooms and fresh coriander.
