Heat a 12-inch skillet over medium-high heat. Add the ground chicken, breaking it up with a spatula, then add the diced green and red bell peppers and diced onion.
Cook, stirring occasionally, until the chicken is cooked through and the vegetables begin to soften, about 6–8 minutes.
Drain the pineapple chunks slightly if very wet, reserve the juice, then add the pineapple to the skillet and stir to combine with the chicken and vegetables.
In a mixing bowl, whisk together 1/2 cup pineapple juice, rice vinegar, dark brown sugar, ketchup, and soy sauce until smooth.
Pour the sauce into the skillet and cook for 2–3 minutes, stirring, to let the flavors meld.
In a small bowl, whisk the cornstarch with the cold water until fully dissolved, then add this mixture to the skillet.
Cook, stirring, for 1–2 minutes more until the sauce thickens and coats the chicken and vegetables.
Remove from heat and serve the sweet and sour ground chicken over white rice.