Heat olive oil in a large pan on medium-high heat. Add onion and cook 6 minutes, stirring often, until fragrant. Stir in beef, salt and pepper. Cook 6–8 minutes, until meat is browned and mostly cooked through.
Add meat mixture to a large pot. Stir in chicken and beef stock, tomato paste and barley. Cook according to barley package directions (about 10 minutes). Stir in vegetable medley and cook 10 minutes more on medium heat. Remove from heat immediately and leave uncovered to prevent vegetables from overcooking.
