How to Make It
Preheat oven to 350°F. Heat 1 Tbsp. oil in a large skillet over medium-high heat. Season chicken with salt and pepper; cook until brown on all sides, about 5 minutes. Transfer to a 2-quart ovenproof dish.
Heat remaining oil in same skillet over medium-high heat. Add onion and bell pepper. Cook, stirring, until onion is soft and pepper is crisp-tender, about 5 minutes. Add garlic, then cook for 1 minute more.
Add ginger, pineapple, vinegar, sugar and tomato sauce. Bring to a boil. In a small bowl, combine cornstarch and soy sauce; stir into pineapple mixture. Cook, stirring, until sauce becomes translucent, about 1 minute. Pour over chicken; stir to combine.
Cover and bake until chicken is cooked through, about 15 minutes. Serve over rice. Garnish with scallions.