Preheat oven to 425°F. Line a large sheet pan with parchment for easy cleanup.
Cut vegetables into evenly sized pieces. Pat dry so they roast instead of steam.
Whisk olive oil, minced garlic, Italian seasoning, salt, pepper, and balsamic (if using).
Toss broccoli, zucchini, peppers, onion, carrots, and tomatoes with the seasoned oil until coated.
Spread in a single layer on the pan, leaving space between pieces for browning.
Roast 15 minutes. Stir and rotate the pan, then roast 8–12 minutes more until tender and caramelized.
Finish with parsley and adjust salt and pepper to taste. Serve hot.