Coat a 6-quart slow cooker insert with cooking spray.
Place the chicken breasts into the slow cooker.
In a medium bowl, whisk together the cornstarch, brown sugar, soy sauce, orange marmalade, lime juice, ginger, salt, and pepper. Pour over the chicken.
Add the pineapple and mandarin oranges.
Cover and cook for 4–5 hours on Low or for 2–2 1/2 hours on High.