1.Lightly coat large skillet with olive oil and place over medium-high heat.
2.Add single layer of onion slices to skillet and cook briefly until slightly softened and lightly seared on one side; remove to plate. Add apple slices to skillet and cook until softened and lightly seared on one side as well; remove to plate.
3.Reduce heat to low. Add generous amount of additional olive oil and drizzle of white truffle oil to skillet. Add four bread slices and let cook until lightly toasted on underside.
4.Spread each bread slice lightly with red pepper jelly. Top two of bread slices with reduced fat cheddar slices. Cover skillet with lid or foil just until cheese is melted.
5.Add vintage cheddar slices. Top with some of seared apples, adding a few raw apple slices for crunch as well if desired. Top with seared red onions. Drizzle with additional white truffle oil.
6.Invert uncovered bread slices on top to make two sandwiches. Cover skillet and let cook for several minutes, just until vintage cheddar is melted. Serve each on bed of greens.