Heat oven to 350° F.
In small skillet over medium heat, cook pork loin, fatty-side down, 4-5 minutes to brown top and render some fat.
Coat 7-by-11-inch baking dish with cooking spray. Place pork loin in dish.
In small bowl, combine mustard, garlic and rosemary; stir well. Spoon mixture over pork. Transfer to oven and bake 45 minutes-1 hour, until cooked.
When finished, let rest 5 minutes before slicing.