1. Cut pork into 1/4- to 1/2-inch cubes. Put a 10- to 12-inch nonstick frying pan over high heat, add pork, and stir often until meat is gray, 5 to 6 minutes.
2. Add orange peel, 1 cup orange juice, onion, and cumin to pan. Stir often over medium-high heat until liquid has evaporated and meat is lightly browned, about 20 minutes. Add 1/2 cup orange juice, scrape browned bits free, and stir until juice evaporates, about 5 minutes.
3. Add black beans and remaining 1/2 cup orange juice and stir just until beans are hot, about 2 minutes.
4. Serve pork mixture in warm tortillas, adding green onions, sour cream, salsa, and salt to taste. Roll to enclose filling.