Preheat oven to 325 degrees.
Heat vegetable oil in a large pot over medium-high heat.
Cut pork roast into 1-inch pieces and place in a gallon sized Ziploc bag.
Pour cornstarch into Ziploc bag, zip closed and shake until pork is evenly coated with cornstarch.
Carefully add pork a few pieces at a time to hot oil, let cook for 2-3 minutes, remove and place on a plate covered with a paper towel to absorb excess oil. Repeat until all pork has been cooked in oil.
Spray a 9 x 13 inch baking pan with nonstick cooking spray and spread pork in the bottom.
Sprinkle on chopped onion, green pepper, and pineapple chunks. Season with salt and pepper, to taste.
Pour pineapple juice from pineapple chunks into a saucepan over medium heat. Whisk in sugar, apple cider vinegar, ketchup, soy sauce and garlic salt.
Bring to a boil and pour over the pork, vegetables and pineapple. Gently stir to combine.
Place pan in oven for 1 hour, stirring every 15 minutes to continually coat pork in sauce.
Remove from oven and serve over rice.