For the sweet & sour sauce:
Put all ingredients (besides water&cornstarch) into a saucepan, and bring to a boil.
In a small cup, dissolve corn starch into water. Stir into the sauce and simmer for 5 mins, until thickened enough. If you want it runny, add a little more of pineapple juice. Set aside when ready.
Soak the bread cubes into the milk for 5 mins. Squeeze the bread out of milk and transfer into a large bowl.
Add garlic, parsley, flaked fish, egg , breadcrumbs and a pinch of flour. If you like add some orange zest and grated ginger. Mix until combined and season.
Shape the fish mixture into small balls. Arrange a plate with some flour and evenly coat each fish balls.
Heat some oil in a frying pan and when hot, throw the fish balls in and cook them until they get a golden color. You can also arrange the fishballs on a tray, brush with oil and bake for 15 min or until cooked through at 170C/350F.
Drain on kitchen paper and transfer into a bowl. Pour some sweet&sour sauce and mix until evenly coated.
Sprinkle with spring onion and sesame seeds, then serve.