Preheat oven to 350°F Lightly coat a baking sheet with cooking spray.
In a bowl, thoroughly mix the milk and prepared brown mustard. In a separate bowl, mix the panko, herbs and garlic. Dredge each turkey breast first in the milk mixture, then in the crumb mixture to evenly coat.
Bake turkey 30 minutes in the preheated oven, until the coating is crisp and the internal temperature of the turkey has reached a minimum of 180°F.
In a bowl, mix the yogurt and whole grain mustard. Season with salt and pepper. Drizzle over the cooked turkey to serve, or use as a dipping sauce.