Preheat the oven to 425°F. Line a large rimmed baking sheet with parchment.
Pat the cauliflower dry. Toss with olive oil directly on the pan.
Combine garlic, paprika, salt, pepper, and red pepper flakes. Sprinkle over cauliflower and toss to coat evenly.
Spread in a single layer. Roast for 15 minutes.
Flip the florets and roast 10–12 minutes more, until edges are deep golden and tender.
Zest and squeeze the lemon over the hot cauliflower. Sprinkle Parmesan and parsley, toss, and serve.