Prepare the chicken by cutting it into bite-sized pieces and seasoning with salt and pepper.
Coat the chicken pieces in flour, shaking off any excess.
Heat the vegetable oil in a large skillet over medium-high heat.
Fry the coated chicken pieces until golden brown and cooked through, about 5-7 minutes per side.
Remove the chicken from the skillet and set aside on a paper towel to drain excess oil.
In the same skillet, add chopped bell peppers, onion, and garlic; sauté for 3-4 minutes.
In a bowl, mix together the rice vinegar, sugar, soy sauce, and sesame oil until well combined.
Add the pineapple chunks to the skillet, followed by the sauce mixture; stir well.
In a small bowl, mix cornstarch with a tablespoon of cold water; add to the skillet to thicken the sauce.
Return the fried chicken to the skillet, coating it well with the sauce.
Let the mixture simmer for 2-3 minutes, then serve hot over rice or noodles.