Preheat the oven to 220˚C/200˚C fan/gas mark 7. Roughly chop 250g cooked, peeled king prawns into 1cm chunks. In a bowl, combine the prawns with 200g cooked crabmeat (fresh or tinned),120g sour cream, 1 finely chopped green chilli, 1 tsp chilli powder, ½ tsp ground cumin and a pinch of salt. Spread 1 x 180g bag of tortilla chips on a large rimmed baking tray. Spread the seafood mixture evenly over the tortilla chips and top with 50g grated mature white Cheddar. Bake in the top half of the oven for 6-8 minutes until the cheese is melted and top with shredded Little Gem lettuce, chopped spring onions and chopped ripe tomatoes.