Heat oil in a small saucepan over medium. Add white scallion slices, and cook 30 seconds. Stir in black beans, taco seasoning, and salt; cook, stirring often, 3 minutes.
While beans cook, prepare rice according to package directions. Stir hot rice into beans, and remove from heat. Stir in green scallion tops. Place 1 cup of hot Rice and Beans in a preheated lunch thermos, and close tightly. Reserve remaining Rice and Beans for another meal.