Prepare the Oven:
Preheat your oven to 400°F (200°C). Line a rimmed baking sheet with foil for easier cleanup, if desired.
Coat the Cauliflower:
Place the cauliflower florets onto the prepared baking sheet. Dollop the pesto over the florets, and sprinkle with salt and freshly ground black pepper. Use clean hands to toss the cauliflower until each piece is well-coated with the pesto.
Roast the Cauliflower:
Spread the coated cauliflower florets into a single layer on the baking sheet. Place the sheet on the middle rack of the oven and roast for 12-15 minutes. Remove the cauliflower from the oven and flip the florets over with a spatula.
Add Parmesan:
Sprinkle the Parmesan cheese evenly over the flipped cauliflower florets. Return the baking sheet to the oven and roast for an additional 10-12 minutes, or until the cauliflower is golden brown and crispy.
Finish and Serve:
Remove the roasted cauliflower from the oven and transfer it to a serving platter or bowl. Squeeze fresh lemon juice over the cauliflower for a burst of brightness. For extra flavor, dollop more pesto and sprinkle additional Parmesan cheese on top, if desired. Serve warm and enjoy!