Preheat the oven to 450°F. Line a baking sheet with parchment paper.
Spread the cauliflower florets over the prepared baking sheet, drizzle with the avocado oil, and season with the salt and pepper.
Toss to coat.
Arrange the florets in an even layer and roast until golden brown and slightly softened, 25 to 30 minutes.
KALE AND WALNUT PESTO
Use your hands to strip the kale leaves from the stems.
Fill a large bowl halfway with cold water and add a couple of hand- fuls of ice. Set it nearby.
Bring a large saucepan of water to a boil. Season with 1 tablespoon salt, add the kale, and blanch for three minutes. Transfer the kale to the ice water and let cool completely, three to four minutes.
Transfer the kale to a colander and squeeze it to drain well. Set aside.
In a small dry skillet, toast the walnuts over medium heat, stirring occasionally to prevent burning, until lightly browned and fragrant, about three minutes.
Transfer the walnuts to a food processor and add the kale, garlic, lemon juice, and a pinch each of salt and pepper. With the food processor running, slowly drizzle in the olive oil until fully incorporated. Taste and adjust the salt and pepper as desired.
Transfer the pesto to a jar, cover, and refrigerate until ready to use. The pesto will keep in the refrigerator for up to 5 days or in the freezer for up to 6 months.
TO SERVE
Transfer the warm cauliflower to a medium bowl and toss with the pesto. Serve immediately.