Combine 1 tablespoon mustard, garlic, thyme and salt and rub all over pork medallions. Heat a large nonstick skillet over medium-high heat until pan is very hot. Add pork and cook 2 minutes each side or until browned. Remove and set aside.
In same skillet, heat olive oil over medium heat. Add onion and cook, 15 minutes, stirring occasionally, until onions are golden and very tender. Add apple slices and cook 3 minutes or until softened. Add apple cider, cider vinegar and remaining mustard and bring to a boil over high heat. Return pork and any juices to skillet and cook 2 minutes or until desired doneness.
Serve pork, onions and apples over hot Riced Butternut Squash. Sprinkle with additional fresh thyme, if desired.