Preheat your oven to 400°F and make the pesto while you’re waiting for it to come up to temperature.
In the bowl of a small food processor, combine the cilantro, garlic, jalapeño, lime juice, nuts, cumin, and 1/2 teaspoon each of salt and black pepper.
Pulse several times. While the machine is running, gradually add 1/4 cup of olive oil through the lid and process until the mixture is fairly smooth, adding additional oil, one tablespoon at a time, as needed for a creamy consistency.
Add the cheese and process for a few seconds more. Add more salt and pepper to taste.
Spread the cauliflower florets in a single layer on a rimmed baking sheet.
Use two baking sheets if necessary to avoid crowding.
Drizzle with the remaining olive oil and season with salt and pepper.
Roast the cauliflower, turning once with a spatula, until lightly brown and tender, about 20 to 25 minutes.
When done, transfer to a large bowl, top with several spoonfuls of the pesto, and use a spatula to coat the florets.
Serve immediately.