Place the chicken in a gallon-size zip lock bag. Add pineapple juice, vegetable oil, soy sauce, brown sugar, and pepper. to the bag.
Secure the bag and gently massage the marinade into the chicken.
Freeze until ready to cook, or marinate 6 hours to overnight.
When ready to cook: Remove chicken from marinade and discard marinade.
Using a sharp knife, cut chicken into bite sized pieces.
Heat the flat top grill, cast iron skillet or wok on high. Add a canola oil and heat.
Add the onions and carrots and cook, tossing frequently until almost tender and caramelized.
Before the vegetables are completely soft, add the cut up chicken. Cook over high heat, tossing frequently until caramelized and cooked through, about 8 - 10 minutes if the heat is high enough.