Cut the sausage, onion and apples into slices/wedges a good size for skewering. Thread loosely onto skewers (can be done ahead as Envy apples discolor very little once cut). Line skewers up flat in a pan or baking dish. In a small bowl, mix together mustard and honey. Spread on top of the skewers, cover and refrigerate for at least 1 hour. Grill the skewers for 10 to 15 minutes, just to heat through and create some caramelization on the onions and apples.