Chicken breast and lean pork often get stringy and a little dry. If you cook them you need to add some kind of fat.
I buy the boneless skinless thighs and use those and they cook up perfect. I put them in right out of the freezer, on top of some frozen veggie, dust the top with garlic powder, a shake of Worcestershire sauce (adds a tang and helps the meat look more appetizingly brown) then add a can of low sodium cream of something soup. mixed with 1/2 can of water. Put the pot on low for 8-9 hours and its done, serve over rice or egg noodles.
I also buy cheap chops with some fat on them and lay them on top of a big onion sliced thick and some water, then cover with BBQ sauce and cook on low 8 hours. They steam up super tender. Micro some corn and have them with a sald. Easy peasy.