Start by marinating the pork pieces in soy sauce, garlic, and ginger for about 15 minutes.
In a large pan, heat vegetable oil over medium-high heat.
Add the marinated pork and stir-fry until browned and cooked through, about 5-7 minutes.
Remove the pork from the pan and set aside.
In the same pan, add diced onions and cook until translucent.
Add bell peppers and pineapple chunks, cooking for another 3-4 minutes.
In a bowl, mix sugar, vinegar, and cornstarch until smooth.
Pour the mixture into the pan and stir well to combine.
Add the cooked pork back into the pan and toss to coat in the sauce.
Season with salt and pepper to taste, then serve hot.