With the tip of a very sharp knife I simply cut an approximately 1/4-inch deep crosshatch design on the cut sides of the zucchini. (It's not as time consuming as it may seem, once you try it you'll be able to prepare many in a short time.)
I usually just season with salt & pepper, sometimes lemon pepper, and a sprinkle of herbs or grated Parmesean cheese, brush with olive or vegetable oil. Grill or broil cut side down first until you achieve the desired grill marks, or lightly browned here and there. Then turn and grill or broil to your liking, but don't over cook ~ the texture is best if they are a bit firm to the bite.
You'll find the zucchini cooks more evenly and quickly this way, and whatever seasoning you use will penetrate the zucchini, to make it more flavorful. These make a fine accompaniment to almost any grilled foods, or simply prepared chicken, fish, chops or steak.