Drain pineapple, reserving ¼ cup juice.
In a bowl, mix 2 tbsp cornstarch, 1 tbsp water, garlic powder, and 1 tbsp pineapple juice. Add pork and toss to coat.
In another bowl, whisk soy sauce, brown sugar, ginger, cayenne, remaining ½ cup water, 1 tbsp cornstarch, and remaining pineapple juice. Set aside.
Heat 1 tbsp oil in a wok/skillet over medium high heat. Stir-fry pork until cooked (3-4 mins). Remove.
Heat remaining 1 tbsp oil. Stir-fry broccoli, carrots, and onion for 5-7 mins until tender crisp.
Whisk sauce and add to skillet. Bring to a boil and cook for 1-2 mins until thickened.
Return pork and add pineapple chunks to skillet. Heat through, about 2 mins.
Serve immediately over rice.