1. If using filleted fish instead of canned fish, poach fish in water in a shallow skillet. To poach, place the fish in a skillet with just enough water to cover the bottom.
2. Cook fish over medium heat. When bottom half is cooked, flip and cook on the other side. When fish is fully cooked and flaky, remove from pan. If necessary, remove the skin, and flake the fish into small pieces. Set aside.
3. Combine the sauce ingredients in a large container. Mix well and set aside.
4. Heat a large and deep frying pan, pot, or wok over high heat. Add oil. Add onion and sauté until mostly soft. Add whatever other vegetables you desire, in the order listed above.
5. When all vegetables are cooked, add the fish and sauce, and cook until thickened.