Spread 1 tablespoon of mayo on one side of each slice of sourdough. Spread 2 tablespoons of cranberry sauce on the other side of 2 of the slices of bread.
In a medium nonstick skillet, toast 1 slice of sourdough (without cranberry sauce), mayo-side down, over medium heat. Stack the slices of turkey, spread 2 tablespoons of gravy in the middle and place 2 slices of cheese on top. Cover for 1 to 2 minutes, until the bread is toasted and the cheese is melted.
Uncover and add ½ an avocado, sliced, and ½ cup arugula on top. Place another piece of bread on top, with cranberry sauce facing the arugula. Flip the sandwich and cook until toasted, about 2 minutes.
Repeat steps 2 and 3 with the second sandwich.
Slice the sandwiches in half and enjoy!