1.
Preheat an outdoor grill for medium heat, and lightly oil the grate.
2.
Slice zucchini lengthwise 1/4 to 1/2 inch thick.
3.
Combine olive oil, salt, garlic, black pepper, and rosemary. Brush on zucchini.
4.
Grill zucchini on both sides until brown. Place on platter and sprinkle with balsamic vinegar.