Preheat a large sauté pan over high heat with 3 turns of the pan of EVOO, about 3 tablespoons. Cook the ground sirloin until browned, 7-8 minutes. Once the meat is brown, season it with salt and pepper.
While the meat is browning, add the oregano, thyme, parsley, garlic and onion to a food processor and pulse the machine to finely chop everything. With the machine running, stream in the vinegar and remaining 1/2 cup of EVOO. Season the herb sauce (in Argentina this is called a chimichurri) with salt and freshly ground black pepper. Add half of the chimichurri to the skillet with the meat, mix to combine.