Drain pineapple juice into a medium sauce pan set over medium-low heat. Reserve pineapple.
Stir in apple cider vinegar, soy sauce, sugar, ground ginger and ¼ cup of water. Continue stirring until sugar has dissolved completely.
In a separate small bowl, mix together 2 tbsp of water and corn starch.
Once sauce has begun to simmer, stir in corn starch mixture. Add diced pepper, onion, pineapple and nuggets. Continue cooking, stirring occasionally, for 10 minutes.