Combine the rosemary and garlic. Make several 1/2 inch deep slits in pork; place about half of the rosemary mixture in slits. Rub pork with remaining rosemary mixture; sprinkle with salt and pepper. Place pork on a jelly roll pan coated with cooking spray. Insert meat thermometer into thickest portion of pork.
Bake at 475 for 20 minutes or until thermometer registers 160 degrees (slightly pink) or desired degree of doneness. Let stand 5 minutes, and cut into 1/4 inch thick slices.