Take 500 grams of boneless fish fillets (preferably white fish like basa or tilapia) and cut them into medium-sized pieces.
In a bowl, mix 2 tablespoons of ginger-garlic paste, 1 teaspoon of red chili powder, 1/2 teaspoon of turmeric powder, 1 teaspoon of coriander powder, salt to taste, and 1 tablespoon of lemon juice. Marinate the fish pieces in this mixture for 20-30 minutes.
Heat 4 tablespoons of oil in a non-stick pan over medium heat. Add 1 teaspoon of mustard seeds and let them splutter.
Add 1 finely chopped onion and sauté until it turns golden brown.
Add 8-10 finely chopped garlic cloves and sauté for 2-3 minutes until the raw smell disappears.
Add the marinated fish pieces to the pan and cook for 5-7 minutes on each side until they are cooked through and slightly crispy.
Add 1/2 cup of water to the pan, cover, and cook for another 5-7 minutes until the fish is tender and the sauce has thickened.
Garnish with chopped coriander leaves and serve hot with steamed rice or roti.