Warm a skillet over high heat. Add a splash of olive oil - coating the pan well.
Spread the vegan butter on both sides of the bread. You can use a bit more for a truly buttery-crusted sandwich.
Place one slice of the bread in the warm pan, rub it into the hot oil a bit and flip it. Then pile the cheese slices on one side.
On the other slice of bread, spread the marmalade.
Sprinkle the walnuts over top the cheese slices - in the pan - and then add the greens and black pepper over top. Then top that with the marmalade-slathered slice.
Using a spatula or heavy pot top, press down on the sandwich. Turn the heat to low and cover the pan with a lid - or the heavy pot lid. Allow to toast and warm for 2-3 minutes.
Flip the sandwich and repeat with pressing down the bread or covering the pan with a lid. The flipped bread side should be lightly browned by now with darker, toasty edges. Give the sandwich another 2-3 minutes to allow the cheese to melt.
When the cheese looks melted and both side toasty, remove from the skillet. Slice and serve.