Remove any silver skin from the pork tenderloin, then cut it in half horizontally. Slice each half into 1/3 inch (8 mm) pieces and place them in a small mixing bowl. Add 2 teaspoons of soy sauce and mix well to coat.

In a small bowl, combine brown sugar, white vinegar, oyster sauce, sriracha, soy sauce, and toasted sesame oil. Stir until the sugar is mostly dissolved. Set aside.

Heat a wok or large pan over high heat. Add the neutral oil. Once the oil is very hot, add the pork in a single layer. Let it cook without stirring for about 1-2 minutes until browned. Toss and stir for about 30 seconds until most of the pork is cooked. Transfer to a bowl and set aside.

In the same wok, lower the heat to medium. Add a little more oil if needed, then sauté the chopped garlic and onion, stirring until the garlic turns golden, about 1-2 minutes.

Increase the heat to high, then add the cucumber, pineapple, bell pepper, and your freshly made sweet and sour sauce. Toss everything together for about 2 minutes until the vegetables are just tender.

Add the pork back into the wok and stir for an additional 30 seconds until heated through. Be careful not to overcook the pork!

Turn off the heat and stir in the cashews and green onions (if using).

Plate up the dish, topping with more cashews and green onions if desired. Serve it over fluffy jasmine rice.