Cut beef tenderloin into 3-ounce medallions and pound to form scaloppini.
In a large bowl, combine 1/4 cup olive oil, garlic, oregano, and 2 tablespoons adobo. Add the meat, stirring to coat evenly. Place in the refrigerator and let marinate for at least 12 hours.
In a saute pan, heat the remaining 1/4 cup olive oil over medium-high heat. Add the onions and saute until golden brown. Add vinegar, chicken stock, and butter, and let simmer for 2 to 3 minutes. Season with 1 tablespoon adobo, or more to taste. Keep warm.
In another large saute pan, heat 2 tablespoons olive oil over medium-high heat. Add beef scaloppini and quickly saute for 2 to 3 minutes on each side. Remove from heat.
To serve, layer the beef scaloppini and the onion mixture and repeat layers 1 more time. Ladle the broth from the onions over top as a sauce. Serve immediately.
*You can use store-bought without MSG.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.