Place the cut chicken pieces in the slow cooker in an even layer.
In a mixing bowl, whisk together 1/2 cup chicken broth, light brown sugar, granulated sugar, white vinegar, lemon juice, soy sauce, tomato paste, garlic powder, ground ginger, black pepper, and Sriracha (if using) until smooth.
Pour the sauce over the chicken, pressing the chicken down so it is covered by the sauce.
Cover and cook on low for 5 to 6 hours, until the chicken is tender and cooked through.
About 20–30 minutes before serving, whisk together 1/3 cup chicken broth and 1/3 cup cornstarch in a small bowl until smooth to make a slurry.
Gently fold the cornstarch slurry into the slow cooker mixture, then add the diced pineapple, diced onion, and diced bell pepper.
Cover and cook on low for an additional 20 to 30 minutes, stirring once or twice, until the sauce thickens and the fruit and vegetables are slightly tender.
Serve warm over white or brown rice.
