Butter 1 side of all bread slices. Spread mustard and jam on the unbuttered sides of 4 slices of bread. Top with arugula, apple slices, 1 slice cheese,1 slice bacon, and another slice of cheese. Add top slices of bread (buttered-sides on outsides)
Cook sandwiches in large non-stick skillet over medium-low heat, in batches if needed, until golden brown before turning to brown second side and cheese is melted. Cut sandwiches in half to serve.
Substitute bacon with ham.