Cook carrots according to package directions. Heat oven to 350 degrees. In a 1 1/2 quart casserole, combine carrots, orange and lemon slices, chopped walnuts and pineapple. Mix pineapple syrup, brown sugar and cornstarch to thoroughly dissolve cornstarch. Pour over casserole; toss carefully to mix. Sprinkle with walnut halves. Bake at 350 degrees for 20 to 25 minutes.