Drain pineapple, reserving 1 tablespoon juice. Discard remaining pineapple juice. Set pineapple aside. Combine reserved pineapple juice, lime juice, fish sauce, sugar, and garlic.
Place reserved pineapple chunks, onion, and the next 4 ingredients (onion through ginger) in a large bowl. Drizzle 2 tablespoons lime juice mixture over onion mixture; toss gently. Combine remaining lime juice mixture with pork, stirring well.
Heat the oil in a large nonstick skillet over medium-high heat. Add pork, and sauté 3 minutes or until done. Add pork to onion mixture; toss well. Serve over arugula.