Step 1: Prepare the Fish
Clean and marinate the rohu fish with turmeric powder and salt for 15 minutes.
Heat 3 tbsp mustard oil in a tawa (pan).
Fry the marinated fish for 2 minutes on each side, then for another 2-3 minutes per side until cooked well.
Remove the fish from the pan and set aside.
Step 2: Make the Mustard Paste
In a jar, combine 1 tbsp mustard seeds, 1 tbsp cumin seeds, garlic, and red chilies.
Add a little water and blend to make a fine paste.
Step 3: Prepare the Gravy
Heat 2 tbsp mustard oil in a kadhai (wok).
Add mustard seeds, cumin seeds, fennel seeds, and fenugreek seeds.
Add sliced onion and cook until translucent.
Add curry leaves and cook for 2 minutes.
Add the prepared mustard paste and cook for a few seconds.
Stir in turmeric powder, salt, and red chili powder.
Add chopped tomato and cook until it softens.
Pour in 1 cup of hot water and bring to a boil.
Add the dry mango and let it boil for 2-3 minutes.
Add the fried fish and cook on medium flame for 3-4 minutes.
Carefully turn the fish and cook for an additional 2-3 minutes on low flame.
Serve the Macha Besara (fish in mustard gravy) hot with rice.