Preheat the oven to 425 degrees F (220 degrees C). Line a baking sheet with parchment paper.
In a large bowl, toss the cauliflower florets with olive oil, salt, and pepper until evenly coated. Spread cauliflower evenly in a single layer on the prepared baking sheet. Set the bowl aside.
Roast in the preheated oven until golden and crispy on the edges, 25 to 30 minutes, turning halfway through cooking time.
Transfer hot cauliflower back to the bowl and toss with pesto and Parmesan cheese. Serve immediately.
