Heat a nonstick skillet over medium heat.
Spread pesto evenly on one side of each slice of bread.
Layer turkey, Swiss cheese, and spinach on one slice of bread, then top with the second slice (pesto side facing in).
Spray the outside of each slice of bread with cooking spray.
Grill the sandwich for 2–3 minutes per side, or until the bread is toasted and the cheese is melted.
Slice in half and enjoy warm.