Whisk together the mayo, garlic, and rosemary in a bowl. Season with salt and pepper to taste.
Preheat a panini style grill. Lightly grease it with nonstick spray.
Spread the mayo on all slices of bread. Layer with cheese, spring mix, turkey, onion, tomato, and cheese.
Cook on the panini grill until golden brown and the cheese is melted. (Alternatively place on a baking sheet and cook in a 350 degree oven using a heavy oven safe skillet or pan to press the sandwich down until the cheese is melted and the sandwich is crispy).