Remove any silver skin from the pork, then cut the tenderloin in half horizontally and slice each half into 1/3-inch slices. Place in a small mixing bowl and toss with 2 teaspoons soy sauce to coat evenly.

In a small bowl, combine the 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 a large skillet) over high heat and add 2 tablespoons neutral oil. Once hot, add the pork in a single layer. Let it cook undisturbed for about 1-2 minutes until browned. Toss and stir for another 30 seconds until mostly cooked through. Transfer the pork to a bowl, leaving behind any oil and juices in the wok.

Reduce the heat to medium and, if needed, add a touch more oil. Add the chopped garlic and sliced onions, stirring until the garlic is fragrant and golden, about 1-2 minutes.

Raise the heat back to high, throwing in the cucumber, pineapple, and bell peppers along with the sweet and sour sauce. Toss everything together for about 2 minutes, allowing the beautiful flavors to mingle and soften slightly.

Add the cooked pork back to the wok, stirring until everything is heated through—this should take another 30 seconds.

Stir in the cashews and garnish with chopped green onions if using. Serve with jasmine rice.