1place 1 slice of the bread on a work surface. Top with the roast beef, tomato slices, avocado slices, and arugula. Spread the remaining bread with mustard and set, mustard side down, on the arugula.
2Heat a ridged non stick grill pan over medium heat until hot. Lightly brush outsides of sandwich with the oil and place on pan. Set a heavy- bottomed skillet on top of sandwich and cook for 1 to 2 minutes per side or until toasted warm in the center