1. Marinate fish: Marinate the fish pieces with ginger-garlic paste, salt, and pepper for 15-30 minutes.
2. Cook fish: Heat oil in a pan and cook the marinated fish pieces until they're cooked through. Remove and set aside.
3. Sauté onions and garlic: In the same pan, sauté the chopped onion and minced garlic until tender.
4. Add capsicum and tomato: Add the chopped capsicum and tomato to the pan and sauté until tender.
5. Add chilli sauce and soy sauce: Add the chilli sauce and soy sauce (if using) to the pan and stir well.
6. Combine fish and sauce: Add the cooked fish pieces to the pan and stir well to coat with the sauce.
7. Serve: Garnish with fresh cilantro and serve hot with rice or noodles.