In a gallon sized resealable plastic bag, combine the first 6 ingredients. In a small bowl, whisk together the balsamic vinegar, olive oil, salt, pepper, & garlic powder. Pour over the vegetables in the plastic bag & press out as much air as possible. Seal. Place in the refrigerator and allow to marinate for 30 minutes.
Preheat your grill to medium-high heat. Pour the vegetables in a grill basket. If you don't have one, you can use a tinfoil pan with holes poked in it. Grill for about 15 minutes, stirring occasionally until the vegetables are cooked, and slightly charred on the outside.
This is a great recipe to use with a variety of different vegetables, so have fun with it and switch it up if you want!