1 1-lb. pork tenderloin
2 tablespoons packed light brown sugar, divided
1/4 teaspoon crushed red pepper (optional)
1/4 cup plus 2 Tbsp. beef stock, divided
3 tablespoons tamari or soy sauce
2 tablespoons rice vinegar
1/4 canola oil, divided
1 1/2 cups long-grain white rice
1 large carrot, cut into matchsticks
1 English cucumber, cut into half-moons
Season pork with 1 tablespoon sugar and the crushed red pepper, if desired, in a 5-to 6-quart slow cooker. Add 1/4 cup stock. Cover and cook on low for 5 hours.
Meanwhile, whisk soy sauce, vinegar, 2 tablespoons oil, and remaining 2 tablespoons stock and 1 tablespoon sugar in a small bowl until sugar dissolves; set aside.
Cook rice according to package directions. Meanwhile, slice cooked pork crosswise into 3-inch pieces, then pull pieces apart with two forks to shred.
Heat remaining 2 tablespoons oil in a large skillet over medium-high. Add pork and cook, without stirring, until well browned on bottom, about 3 minutes. Stir in half of the soy sauce mixture and cook until liquid thickens, about 1 minute. Remove from heat.
Spoon warm rice onto serving plates. Top with pork, carrot, and cucumber. Drizzle with remaining soy sauce mixture.