Add chicken, Italian dressing mix, olive oil, lemon juice and garlic to a large zip-top bag. Knead bag to mix well. Marinate in the refrigerator at least 2 hours and up to 2 days.
Meanwhile, wash and slice zucchini lengthwise into fourths and toss with olive oil, kosher salt and pepper; set aside.
When ready to cook, preheat the grill to medium-high heat and lightly oil the grate.
Place chicken breasts and zucchini on the grill and cook about 5-7 minutes per side.
Serve grilled zucchini alongside chicken.
Note: Reserve half of grilled chicken breasts for arugula salad with berries and grilled chicken.
