- 1 (1 1/4 pound) pork tenderloin, trimmed of silver skin
- salt and ground black pepper
- 1/3 cup ketchup
- 1/3 cup seasoned rice vinegar
- 1 (8 ounce) can pineapple chunks, drained with juice reserved
- 2 tablespoons brown sugar
- 4 cloves garlic, minced
- 2 teaspoons hot chili sauce (such as Sriracha®)
- 1 teaspoon soy sauce
- 1 pinch red pepper flakes
- 1 tablespoon vegetable oil
- 1 teaspoon butter
- 1/4 cup chopped green onion (white part only)
- 2 tablespoons chopped green onion tops
- Cut tenderloin into 4 pieces. Arrange in a single layer between two sheets of plastic wrap and pound with a meat mallet until each is about 1-inch thick. Generously season with salt and black pepper.
- Whisk ketchup, rice vinegar, reserved pineapple juice, brown sugar, garlic, hot chili sauce, soy sauce, and red pepper flakes in a bowl. Set aside.
- Heat vegetable oil in a skillet over high heat. Place pork in pan; reduce heat to medium. Cook until browned on both sides and cooked through, 5 to 6 minutes per side. Transfer to a plate.
- Return skillet to medium heat. Stir butter into hot pan. When butter melts and starts to brown, stir in pineapple chunks. Cook, stirring, until pineapple is golden brown, 3 to 4 minutes.
- Stir in ketchup mixture and 1/4 cup green onion (white parts). Reduce heat to low and simmer until garlic and onion have softened, 5 minutes.
- Return pork to skillet; cook, stirring, until pork is heated through. Garnish with 2 tablespoons green onion tops.