Cut up the pork tenderloin into small bite-sized pieces and season with salt and pepper; set aside.
Heat oil in a large skillet set over medium-high heat. Add diced onions to the heated oil and cook for 2 minutes. Stir in garlic and cook for 15 seconds or just until fragrant.
Add the pork to the skillet; season with brown sugar, oregano, chili powder, and cumin. Cook, stirring frequently, for about 10 minutes or until pork is cooked through.
Stir in orange juice; continue to stir and scrape up the browned bits from the bottom of the pan. Add lime juice and continue to cook for 2 more minutes.
Remove from heat. Taste for salt and pepper and adjust accordingly.
Serve in tacos, burritos, over rice, and/or on salads.
Notes
Pork Choice: You don't have to use pork tenderloin. You can also use pork shoulder or any other cut of boneless pork but remember that depending on the cut of pork, you may have to adjust the cooking time.
Don't Overcook: You want the pork to be juicy and tender, not tough and dry. The best way to gauge if pork is done is to use a meat thermometer - pork is cooked through when its internal temperature reaches 145˚F.
Shredded Pork Method: Season the pork tenderloin thoroughly with all the spices before slicing it into pieces. Once cooked thoroughly, shred the pork using two forks or chop it finely with a knife. Afterward, return the pork to the skillet and let it simmer in the orange juice as instructed.