Whisk together olive oil, balsamic vinegar, garlic, Italian seasoning, salt, pepper, and red pepper flakes.
Add chopped vegetables and toss until coated; marinate 20 min – 2 hr.
Thread vegetables onto skewers, alternating colors; brush with remaining marinade.
Preheat grill to 400°F, clean and oil grates.
Grill kabobs 10–12 min, turning every 3–4 min until tender and lightly charred.
Let rest 2 min; garnish with parsley and lemon wedges.
Enjoy immediately with your favorite BBQ sides.