Start by cleaning and patting dry the fish fillets/pieces.
In a medium to large bowl (depending upon fish quantity), place the fish pieces.
Add in spices such as turmeric powder, red chilli powder, fish fry masala - (optional) and salt to taste.
Add mustard oil to the bowl and mix well to create a marinade. Cover the mixture with a lid and keep the marinate aside for 30-45 minutes.
Heat oil in a deep-frying pan or kadai over medium heat.
Place the marinated fish into the hot oil, being careful not to fill up the pan completely.
Cook the fish for 4-5 minutes per side, or until golden brown and crispy.
Use a spoon or tongs to flip the fish fillets. When the fish is fried perfectly, place fish pieces on paper towels to drain any extra oil.
Once all the fish pieces are cooked, arrange the fish on a platter and garnish with fresh herbs or lemon wedges (optional though).