Combine jalapeño, garlic, anchovy, lime juice, salt, pepper, and cumin in a small bowl. Slowly drizzle in olive oil while whisking constantly until all has been added. Taste and add more salt or lime juice as needed.

Bring a large saucepan of heavily salted water to a boil over medium-high heat. Add cauliflower and cook until just tender, about 3-4 minutes. Drain and immediately toss with the dressing. Garnish with scallions and serve.