Prep all ingredients: cut chicken into bite-size pieces, chop onions and bell pepper, mince garlic, and dice pineapple; whisk together chicken broth, vinegar, soy sauce, ketchup, Truvia, granulated sugar, 2 tablespoons cornstarch and a pinch of garlic powder until smooth to make the sauce.
Season the chicken on both sides with salt, pepper, and 1/2 teaspoon garlic powder.
Heat a large nonstick skillet over medium-high and add 1/2 tablespoon vegetable oil (and cooking spray if desired). Add the chicken and cook, stirring occasionally, until browned and cooked through, about 5–7 minutes.
Add the chopped red onion and bell pepper to the skillet (reserve the pineapple). Cook 2–4 minutes until vegetables are crisp-tender or longer to preferred doneness.
Pour the prepared sauce into the skillet, bring to a boil, and cook until the sauce thickens, stirring frequently, about 1–3 minutes.
Stir in the diced pineapple, heat through for 1 minute, then remove from heat.
Divide into four equal portions and serve over rice if desired.