Preheat oven to 425°F. Line a large sheet pan with parchment.
Dry the green beans well with towels so they roast, not steam.
Toss beans with olive oil, garlic, salt, and black pepper until evenly coated.
Spread in a single layer on the pan. Roast 12 minutes, stirring once halfway.
Sprinkle Parmesan over the beans. Toss lightly, then roast 4 to 6 minutes until golden and tender-crisp.
Finish with lemon zest and red pepper flakes. Serve hot.