Heat oven to 425°F. In large bowl, mix 1 tablespoon oil, 1 teaspoon Italian seasoning, 1/4 teaspoon salt and the garlic. Add sweet potatoes and onions; toss to coat. Spread in 9x13-inch pan. Roast uncovered 10 minutes.
Meanwhile, brush pork tenderloin with 1/2 tablespoon oil. In small bowl, stir together 1 teaspoon Italian seasoning, 1/4 teaspoon seasoned salt and the Parmesan cheese.
Move vegetables to center of pan; place pork tenderloin on one side. Sprinkle seasoning mixture evenly over pork. Insert ovenproof meat thermometer so tip is in thickest part of pork.
Roast uncovered 20 to 25 minutes longer or until thermometer reads 155°F. Cover pan with foil; let stand 5 minutes or until thermometer reads 160°F. (Temperature will continue to rise about 5°F, and pork will be easier to carve.)
Cut pork into 1-inch-thick slices; arrange on platter with sweet potatoes and onions. Sprinkle with parsley.