How to Make It
Combine roasted bell pepper, shallot, chile, garlic, paprika, 1 tablespoon of the vinegar, 2 tablespoons of the oil, and 1⁄2 teaspoon of the salt in a food processor. Process until smooth, stopping to scrape down sides of the bowl, if needed.
Pat steak dry; sprinkle both sides with pepper and 1 teaspoon of the salt. Heat 1 tablespoon of the oil in a large cast-iron skillet over high. Add steak to skillet; cook to desired degree of doneness, 4 to 5 minutes per side for medium. Transfer to a cutting board; let rest 10 minutes.
Meanwhile, chop scallions, keeping white and green parts separate. Wipe skillet clean. Heat 3 tablespoons of the oil in skillet over high. Add white scallion parts; cook, stirring often, until slightly softened, 2 minutes. Add riced cauliflower and remaining 1 teaspoon salt; cook, stirring often, until cauliflower is tender, about 5 minutes. Remove from heat; stir in parsley.
Whisk together remaining 1 teaspoon each of oil and vinegar in a bowl. Add arugula; toss to coat. Cut steak across the grain into thin slices.
Divide cauliflower rice evenly among 4 bowls; top with steak, arugula, and sauce. Sprinkle with green scallion parts.