Heat oven to 425°F. In ungreased 15x10x1-inch pan, place pork. Insert meat thermometer horizontally into center of thickest part of pork.
Cut potatoes and zucchini lengthwise in half. Arrange potatoes, zucchini and onions around pork. Drizzle butter over vegetables; sprinkle with thyme and lemon-pepper seasoning.
Bake uncovered about 35 minutes or until thermometer reads 155°F. Loosely cover pan with foil and bake 10 to 15 minutes longer or until thermometer reads 160°F and vegetables are tender. Cut pork into thin slices. Serve with vegetables.