Prepare the sauce by placing the sugar, vinegar, soy sauce, chicken stock, and tomato sauce into a medium frying pan. Bring to a boil, then reduce the heat to low and set aside.
In a bowl, add the beaten egg and fish fillets, mixing to coat the fish evenly. Add the cornflour and mix until the fish is fully coated.
Heat a non-stick medium frying pan over medium heat. Add the fish and cook for 2–4 minutes, or until almost cooked through. Remove from the pan and set aside.
Meanwhile, cook the rice according to the packet instructions. Once cooked, slice the fish into cubes.
In the same frying pan, add the capsicum and cook for 3–5 minutes, or until softened. Add the pineapple, prepared sauce, and fish to the pan, and continue cooking until the fish is fully cooked through.
Serve the fish with rice and garnish with sliced spring onions. Enjoy!