Preheat oven to 350 degrees F (175 degrees C). Line a baking sheet with parchment paper. Grease with cooking spray.Advertisement
Mix mayonnaise, Dijon mustard, rosemary, garlic powder, salt, and pepper together in a bowl.
Season chicken breasts lightly with salt and pepper. Arrange seasoned-side down on the baking sheet. Spread 1/4 of the mayonnaise mixture over each chicken breast with a spatula.
Bake in the preheated oven until center is no longer pink and top is lightly browned, about 35 minutes. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).
Use light mayonnaise if desired.
Substitute dried rosemary for the fresh if desired.