Prepare the ingredients by dicing the chicken and chopping the vegetables.
In a small bowl, combine cornstarch with water to create a slurry.
Heat vegetable oil in a large skillet or wok over medium-high heat.
Add diced chicken to the skillet, season with salt and pepper, and cook until golden on all sides.
Once the chicken is cooked, add the chopped onions and bell peppers to the pan, stirring until tender.
Stir in the pineapple chunks, sweet & sour sauce, and soy sauce.
Add the cornstarch slurry to the skillet and mix well.
Cook for an additional 2-3 minutes, allowing the sauce to thicken, then remove from heat.
Serve the sweet & sour chicken hot over rice or noodles.