Preheat the oven to 180C/Gas 4.
1) In a large baking tray or cast iron pan place a layer of the tortilla crisps and cover with the shredded Cheddar and Pepper Jack cheeses. Bake the crisps for 2 to 3 minutes, or until the cheeses are melted. Remove the dish from the oven and set aside.
2) In a large saute pan over medium-high heat, melt the butter and saute the garlic until soft. Add the crabmeat, prawn, and scallops and saute for 3 minutes.
3) Add the cream, garlic powder, Parmesan, salt and pepper, to taste, to the seafood and stir for 2 to 3 minutes, until the sauce has thickened.
4) Remove the seafood mixture from the heat and pour over the tortilla crisps. Top the nachos with shredded lettuce, pico de gallo, jalapenos, and a large dollop of soured cream. Serve immediately.