Cut tenderloin into thin, 1/4-inch strips, trimming off all fat. Pound out slices, maintaining the rectangular shape, until they are approximately 1/8" thick. Whisk together soy sauce, sugar, salt and mirin until dissolved. Dip slice of steak in soy mixture then place a piece of scallion, pepper and jicama on top. Roll tightly and skewer through center.
Grill or broil, over or under medium-high heat, basting with sauce, for 3 or 4 minutes. Cut each roll in 2 or 3 pieces and skewer with toothpick. Serve warm or room temperature.