Pat the fish fillets dry with paper towels.
Heat vegetable oil in a skillet over medium heat.
Add garlic and grated ginger and sauté for about 30 seconds until fragrant.
Stir in mustard paste, turmeric powder, chili powder, salt, and black pepper.
Add water or fish stock and stir to create a smooth sauce.
Bring the sauce to a gentle simmer.
Place fish fillets carefully into the sauce.
Cover and cook for about 8–10 minutes until the fish becomes tender and flakes easily.
Drizzle lemon juice over the fish before serving.
Garnish with fresh cilantro and serve hot.