Wash and dry the cauliflower thoroughly. Remove the leaves and core, then cut it into florets.

Pulse the florets in a food processor until it has the texture of rice. (Do this in batches to prevent it from becoming mushy. If you don’t have a food processor, you can grate the cauliflower using a box grater.)

Heat olive oil in a large skillet over medium heat. Add the cauliflower rice and cook for 5–7 minutes, stirring occasionally, until tender but not mushy.

Stir in Parmesan, basil, walnuts, salt, and pepper. Cook for 1–2 more minutes, allowing the flavors to combine. Finish with a squeeze of lemon juice before serving.