Heat olive oil in a large skillet over medium-high heat. Add the onion, and cook for a few minutes, then stir in the beef, and garlic. Cook, stirring frequently until meat is evenly browned.
While the meat is cooking, stir together the lime juice, jalapeno, cilantro and green onion. When the meat is browned, stir in the cilantro mixture and oregano. Pour in the salsa, cover and cook for about 10 minutes, stirring occasionally, until the meat is cooked through.