Heat oven to 450°F. Spray 15x10x1-inch pan with cooking spray. Place pork tenderloin in pan. In small bowl, mix rosemary, salt, sage and pepper. Rub half of seasoning mixture on pork.
In medium bowl, toss sweet potato, pears and onion with oil until coated. Sprinkle with remaining seasoning mixture; toss. Place vegetables around pork.
Bake 25 to 30 minutes, stirring vegetables and pears gently once or twice during baking, until pork has slight blush of pink in center and meat thermometer inserted in center reads 145°F, and vegetables are tender. Remove from oven; cover with foil and let stand 3 minutes before slicing. Cut pork into 1/2-inch slices. Serve with vegetables. Garnish with fresh sage leaves.