In a medium bowl, whisk together all of the sweet and sour ingredients.
Chop broccoli into bite size pieces.
Roughly chop up the bell pepper.
In a large frying pan, over medium heat, heat vegetable oil.
Add the meatballs; brown on all sides for about 5 minutes.
Move the meatballs to the edges and add the broccoli, red bell pepper and the pineapple pieces: stir fry for a few minutes until they start to brown.
Pour in the sauce; allow to simmer for a few minutes, stirring all the time, until it thickens up and the meatballs are cooked through.
Sprinkle the spring onion and the sesame seed over the top.
Serve immediately with hot steamed rice (if using as an entrée) or use an appetizer without the rice.