Place your vermicelli nests in a pan and pour over some boiling water from the kettle. Simmer them for 2-3 minutes, then drain them and rinse under cold water to stop the cooking process. Put to one side.
Whilst the vermicelli is cooking, start on the sauce. Heat 1tbsp of the oil in a wok and fry the onions on a medium heat for 3-4 minutes until they start turning translucent. Add in the chillies, ginger, garlic and shrimp paste. Cook for a further 2-3 minutes, stirring regularly.
Remove from the heat and blend the onion/chilli mixture in the pan using a hand blender (be careful, it will be hot and it may splatter a little - transfer to a food processor to blend if you prefer). Once blended, stir in the yellow bean paste, tamarind paste, fish sauce and sugar. Scoop out the mixture and place in a bowl.
Heat half a tbsp. of oil (in the same wok) until hot and then add in half of the egg/soy sauce mix. Swill around the pan to make a thin omelette. Turn over after a minute and cook the other side. Slide out of the pan onto a cutting board and repeat with the remaining egg (use another 1/2 tbsp. oil if you need to). Place the second omelette on top of the first, then roll them up and slice - to give you long, thin slices. Put to one side.
Heat the remaining oil and add in the king prawns, cook for 2 minutes until pink (if they're already cooked, then heat for 2 minutes anyway to heat through). Add in the tiny shrimps and beansprouts and cook for a further minute. Add in the chilli/onion paste and heat for a minute or two until bubbling. Add in the noodles and soy sauce, then heat on high (moving around the pan often) for another couple of minutes until the noodles are heated through.
Divide between bowls, and top with the cooked omelette (the heat from the noodles will be enough to ensure the omelette slices are warm).
Sprinkle on some chopped spring onions/scallions and fresh chilles, then garnish with lime wedges.