Preheat an outdoor grill for medium-low heat and lightly oil the grate.
Brush zucchini with olive oil. Sprinkle Italian seasoning, garlic powder, and salt over zucchini.
Cook on the preheated grill until beginning to brown, 3 to 4 minutes per side. Brush balsamic vinegar over zucchini and continue cooking 1 minute more. Serve immediately.