In a bowl, mix together the flour, cornstarch, a large pinch of salt and several grinds of black pepper. Add the pork and toss until coated thoroughly. Set aside for 15 minutes.

Add a good glug of veg oil to a large nonstick pan on high heat. Shake any excess coating off the pork cubes and fry them for 6 to 8 minutes until cooked, dark brown, and crunchy. Remove the cubes to a paper-towel lined plate, and give them a light sprinkle of salt.

Add the onion, garlic, ginger, and green onion to the pan. Let fry 1 minute, then add the bell peppers and fry another 2 minutes.

Turn the pan down to medium. Add the rice vinegar, ketchup, soy, chili sauce, and pineapple juice to the pan and bring to a simmer. Stir in the pineapple chunks. Make a slurry from the remaining cornstarch plus a few tbsp water. Stir the slurry into the sauce and simmer 1 to 2 minutes until thickened. Plate the pork and pour the sauce over, or serve the sauce on the side.