1. Combine first 4 ingredients, stirring with a whisk.
2. Cut pork crosswise into 8 pieces. Place pork pieces between 2 sheets of heavy-duty plastic wrap; pound each piece to 1/2-inch thickness using a meat mallet or small heavy skillet.
3. Heat a large nonstick skillet over medium-high heat. Coat pork generously with cooking spray; add to pan. Cook 3 minutes on each side or until done. Remove pork from pan; place on a serving platter. Add mirin mixture to pan. Cook 2 minutes or until mixture thickens slightly.
4. Return pork and accumulated juices to pan. Cook 2 minutes, turning pork to coat. Serve pork with sauce and Pineapple Salsa.