Add pork tenderloin to a large resealable plastic bag. In a medium bowl, whisk all marinade ingredients. Pour marinade into plastic bag, seal tightly and toss to coat tenderloin in mixture. Refrigerate for at least 2 hours.
Remove pork from bag; discard marinade. Preheat your outdoor gas grill (or indoor grill pan) over medium-high heat until hot, about 5 minutes. Place pork on grill and cook, turning occasionally, until golden and grill-marked, about 20 minutes. Pour beans into a cast iron pot, cover and place directly on grill. Stir beans occasionally for 20 minutes while pork cooks alongside.
Once pork is close to done, a thermometer inserted into center of meat should register 140°F. Transfer pork to a cutting board, cover loosely with aluminum foil and let rest for 10 minutes. Carefully remove beans and set aside.
Meanwhile, place orange slices on the grill and cook, turning once, until nicely grill-marked, 1 to 2 minutes per side. Slice pork and arrange on a platter. Garnish with orange slices and rosemary sprigs. Serve immediately with beans.