Heat a griddle pan over a high heat. Brush the steaks with a thin layer of oil and place onto the hot pan for 3 minutes per side for medium, or longer if preferred. Remove the meat and cover. Rest for 10 minutes then slice.

?While the meat is resting, toast the slices of bread on the same griddle pan.?Mix the mustard and mayonnaise together.?Assemble the sandwich by placing a slice of Cheddar and some steak on one slice of bread. Top with another slice of bread. Spread with the mustard-mayonnaise mixture. Add sliced tomato and salad leaves and top with a third slice of bread. Serve immediately.