Preheat oven to 425°F. Line a rimmed sheet pan with parchment for easy cleanup.
Trim zucchini ends and cut into 0.5-inch thick coins or spears.
In a large bowl, toss zucchini with olive oil, garlic, lemon zest, salt, black pepper, and red pepper flakes.
Spread in a single layer on the sheet pan, leaving space between pieces.
Roast for 12 to 14 minutes, then sprinkle evenly with Parmesan and continue roasting 5 to 7 minutes until tender with golden edges.
Optional: Broil for 1 to 2 minutes for extra browning. Garnish with parsley and serve hot.
Notes
For best texture, avoid overcrowding the pan. Try finishing with a squeeze of fresh lemon juice. Leftovers keep up to 3 days in the fridge; reheat in a hot oven or air fryer.