Cut zucchini into slices, making sure the slices are the same thickness. Combine salad dressing with garlic powder and dried herbs of your choice, if using. (I like this both with and without the extra flavorings. This is one place where fresh herbs are not better.) Put zucchini slices into ziploc bag, pour in marinade and let zucchini marinate 4 hours or longer, even as long as all day if desired.
To cook zucchini, preheat grill to medium-high. (You can only hold your hand there for 3-4 seconds.) You can spray the grill with non-stick spray if desired, but you don't really need it.
Place zucchini on grill, having a spray bottle handy for taming any flames that shoot up from the oil in the marinade. After about 4 minute, check for grill marks, and rotate zucchini a quarter turn. Cook 3-4 more minutes on first side.
Turn zucchini to second side and cook about 4 minutes more, or until zucchini is starting to soften quite a bit, with the outside slightly charred and browned. Season with salt and fresh ground black pepper and serve hot.