To make the sauce, mix the cornflour with a tablespoon of pineapple juice and mix well to get a runny paste.
Add the rest of the pineapple juice, ketchup, vinegar, brown sugar, and soy sauce, and mix well.
Heat up the oil in a large pan.
Peel and chop the onion, and fry until golden.
Add the chopped peppers, and give it a good stir, then leave to cook for 2-3 minutes to soften slightly.
Add the cubed pork and sauce, and stir again.
Leave it to simmer for 4-5 minutes for the sauce to thicken and coat the pork and veggies well.
Add the cubed pineapples, give it a stir, then remove from the heat.
Serve on a bed of rice with fresh parsley.