Combine oil, turmeric, galangal, garlic, shallots, salt, sugar, and fish sauce in large bowl and mix well. Marinade the fish nuggets in the fridge for minimum 30 minutes.
Make the mam nem sauce and boil the vermicelli noodles and set aside.
Add about 3-4 tbs of cooking oil deep cast iron skillet. Get the oil nice and hot to about 350 degrees. Rinse off excess marinade and pan fry the fish, flipping to make sure they are browned both sides. When they are just just about done, add the onions and the dill and scallions and gently pan mix without breaking fish. Cook until herbs and onions have softened about another minute. Remove from heat and garnish with peanuts and serve immediately with vermicelli noodles, fresh herbs, and mam nem sauce.
The trick with this dish is to cook the fish nuggets without breaking them. Don't use too flaky delicate fish. You can drain out excess oil before adding the herbs.