Heat oven to 425°F. Line a large rimmed baking sheet with parchment.
Prep the vegetables. Slice zucchini into half-moons and halve the tomatoes.
Toss zucchini with olive oil, garlic, Italian seasoning, salt, black pepper, and red pepper flakes.
Spread zucchini on the sheet in an even layer. Roast 10 minutes.
Add tomatoes to the pan, drizzle with balsamic if using, and toss gently. Roast 8–12 minutes, until tender and lightly browned.
Finish with lemon zest, Parmesan, and basil. Taste and adjust seasoning, then serve hot.