For marinade, place peppercorns in small skillet.
Shake over medium-low heat, shaking skillet often, until fragrant, about 2 minutes.
Let cool.
Crush peppercorns with mortar and pestle (or place between paper towels and crush with a hammer).
Transfer to medium bowl.
Add 2 teaspoons of the soy sauce, 2 teaspoons of the sherry, 1 1/2 teaspoons of the vegetable oil and the cornstarch; mix well.
Cut pork into 1/8 inch thick slices, then cut into 2 x 1/2-inch pieces.
Add to marinade and stir to coat well.
Let stand 30 minutes.
Combine remaining 2 teaspoons soy sauce, 2 teaspoons sherry, the vinegar and sugar in small bowl; mix well.
Heat remaining 6 teaspoons vegetable oil in wok or large skillet over high heat.
Add garlic and stir once.
Add pork and stir-fry until meat is no longer pink, about 2 minutes.
Add yellow onion and stir-fry 1 minute; add green onion and stir-fry 30 seconds.
Add soy-vinegar mixture and cook 30 seconds.
Stir in sesame oil.