Preheat the oven to 425 degrees F.

Place the cauliflower on a large rimmed baking sheet. Drizzle with 1 tablespoon olive oil and season with ¼ teaspoon salt, and ¼ teaspoon pepper. Toss it with your hands to coat it well with the oil then spread out evenly over the baking sheet. Roast for 12 to 14 minutes (no need to stir), or until beginning to brown and barely fork tender. Remove from the oven, toss with a spatula, and set aside.

Meanwhile, heat the remaining 1 tablespoon oil in a 12-inch oven-safe skillet over MEDIUM heat. Add the onion and bell pepper and cook, stirring, 3 to 4 minutes, until softened. Add the beef and cook, stirring to break up the beef, until it is cooked through, about 5 minutes. Drain off the excess grease from the skillet and return it to the heat. Stir in the garlic, chili powder, cumin, oregano, smoked paprika, remaining ¾ teaspoon salt and ¼ teaspoon black pepper and the cayenne pepper (if using). Cook, stirring, for about 1 minute. Add the tomatoes and their juices and the roasted cauliflower. Increase the heat under the skillet as needed until you hear it bubbling. Then, immediately reduce the heat to LOW, cover, and simmer for 5 minutes, or until the cauliflower is tender.

Meanwhile, set the oven to BROIL with a rack in the upper third of the oven. Sprinkle the cheese over the beef mixture. Transfer the skillet to the oven and cook until the cheese has melted and it is lightly browned in spots, about 3 minutes.

Remove from the oven and garnish with cilantro, green onions, pickled jalapenos, and sour cream.