To make the pork chops: Combine sherry, pepper, 1 tbsp of the soy sauce and 1/2 tsp of the sugar in a medium bowl. Add pork and gently toss until well coated. Let marinade in the refrigerator.
Stir together pineapple juice, ketchup, vinegar, the remaining tbsp of soy sauce and remaining tsp of sugar in a small bowl until well combined.
Heat 1 tbsp of the oil in a large, nonstick skillet over medium high heat until hot but not smoking. Add onion and cook, stirring occasionally, until browned but still a little crisp, about 2 minutes. Transfer to a large dish. Heat another tbsp of the oil in the same skillet over medium high heat until hot but not smoking. Add peppers and cook, stirring occasionally, until browned but still a little crisp, about 3 minutes. Transfer to the same dish.
Heat remaining tbsp of oil in the same skillet over medium high heat until hot but not smoking. Add the pork cubes, arranging in a single layer. Cook, undisturbed, until a golden brown crust forms on the bottom, about 1 1/2 minutes. Turn the cubes over and cook until a golden brown crust forms on the other side, about 1 1/2 minutes.Return onion and peppers to the pan and toss to combine. Add pineapple juice mixture and cook, stirring, until sauce evenly coats everything and thickens slightly, about 2 minutes. Serve immediately.
For the brown rice: In a saucepan, bring the stock to a boil and add the rice. Cover with lid and let simmer for 20-30 minutes. Using a fork, fluff the grains and serve.
Should be 1 1/2 cups brown rice but it kept leaving that measurement out!