Twist the coriander leaves away from the stalks to remove, then put the stalks in a bowl and bash a few times with the end of a rolling pin to bruise them. Zest and juice the limes into a non-metallic bowl. Finely grate in the ginger and garlic, then the frozen chillies (try a little of the chilli to see how hot it is first – you may only need 1 chilli if very hot). Add the sugar and 1 tsp salt, and stir to dissolve. Cover the bowl and chill overnight, or for at least 2 hrs, to let the flavours infuse.

Remove the black seam that runs along the belly of each prawn by making a small slit with your knife and pulling it out. Cut each prawn into 3-4 pieces. Heat a frying pan over a low-medium heat and cook the prawns until they just turn lightly pink, no more than 1-2 mins.

Strain the spiced lime juice through a fine sieve or muslin into a large bowl. Add the prawns and toss well to coat. Cover and chill for 30 mins-1 hr, stirring every now and then, until cold.

Add the chopped onion, avocado and tomatoes, chill for another 30 mins, if you have time, or serve straightaway. Roughly chop the coriander leaves and stir through the ceviche, then pile onto a large sharing plate, scatter with the sliced chilli and serve with the tortilla chips for scooping.