Place the meat in the crockpot, pour onions over the top of the meat. Cover with the pineapple juice and 1/2 cup of the teriyaki sauce. Cover and cook on low for 7-8 hours or high 4-5 hours. I turned the meat over half way through cooking to coat both sides in the sauce. Or if you plan ahead you could even try marinating it!

Once the meat is cooked shred it, and pour the remaining 1/4 cup of teriyaki sauce and stir to coat.