In a small bowl, mix the light mayonnaise, Dijon mustard, and pinch of garlic powder.
Lay the bread slices on a flat surface. Spread the dressing on one slice of bread, then top it with the Swiss cheese and turkey breast.
If you're using a panini press, start by preheating the device. Once it's ready, Spray it with nonstick cooking spray and place your assembled sandwich inside the press. Carefully close the lid. Let the sandwich cook for 3 to 5 minutes or until it has a crispy, golden exterior and the cheese inside has melted. If you don't have a panini press, you can cook it on the stovetop. Heat a nonstick skillet over medium heat and spray it with nonstick cooking spray. Place the assembled sandwich in the pan, and use another heavy skillet to press down on it. Cook the sandwich for 3-4 minutes on each side or until it has a crispy, golden exterior and the cheese inside has melted.