In a small mixing bowl, whisk together the 3 tbsp soy sauce low-sodium preferred, 2 tbsp pineapple juice from the fresh pineapple, 2 tbsp brown sugar, 1 tbsp rice vinegar, 1 tbsp cornstarch, and 1 tsp sesame oil until the 1 tbsp cornstarch is fully dissolved and the sauce is smooth. Set aside.

Heat 2 tbsp vegetable oil of vegetable oil in a large wok or skillet over high heat until shimmering. Add the 1 ¼ lb pork tenderloin thinly sliced against the grain into ¼-inch strips strips in a single layer and cook undisturbed for 1–2 minutes until browned on one side, then stir-fry for another 1–2 minutes until just cooked through. Transfer the 1 ¼ lb pork tenderloin thinly sliced against the grain into ¼-inch strips to a plate and set aside.

Add the remaining 2 tbsp vegetable oil of vegetable oil to the same wok over high heat. Add the 1 medium yellow onion wedges and 1 large red bell pepper seeded and cut into 1-inch pieces and 1 large green bell pepper seeded and cut into 1-inch pieces and stir-fry for 3–4 minutes until they begin to soften but still have a slight crunch. Add the 3 cloves garlic and 1 tbsp fresh ginger peeled and finely grated and stir-fry for 30 seconds until fragrant. Add the 2 cups fresh pineapple chunks and toss to combine, cooking for 1 more minute.

Return the cooked 1 ¼ lb pork tenderloin thinly sliced against the grain into ¼-inch strips to the wok. Give the sauce a quick stir to re-dissolve the 1 tbsp cornstarch, then pour it over everything. Toss and stir-fry for 1–2 minutes until the sauce thickens and coats all the ingredients evenly. Remove from heat.

Spoon the pineapple 1 ¼ lb pork tenderloin thinly sliced against the grain into ¼-inch strips stir fry over 2 cups cooked white rice steamed steamed. Garnish with sliced green onions thinly sliced and 1 tbsp sesame seeds for garnish if desired. Serve immediately.