Sweet & Sour Meatballs

Ingredients
2 tbsp vegetable oil
500g (1 lb) pre-made mini meatballs
1 onion, sliced
1 capsicum (bell pepper), cut into bite-sized pieces
1 cup diced fresh pineapple
4 spring onions (scallions), trimmed, green and white parts cut into 3cm (just over 1”) batons
steamed rice, to serve
Sweet & sour sauce:
½ cup brown sugar
3 tbsp white vinegar
2 tbsp tomato ketchup
1 tbsp light soy sauce
1/3 cup pineapple juice
¼ tsp Chinese five spice
2 tsp cornflour (cornstarch), mixed with 2 tbsp water