Whisk red wine vinegar, 2 teaspoons cornstarch, kosher salt, and pepper together in a glass or ceramic bowl. Add beef to vinegar mixture and toss to coat. Marinate meat for at least 20 minutes. Drain beef and discard marinade.
Heat vegetable oil in a large skillet over medium-high heat. Cook and stir beef and onion in hot oil until meat is browned and onions are soft and translucent, 5 to 10 minutes.
Stir water, Worcestershire sauce, soy sauce, garlic, and beef bouillon together in a pot over medium-high heat until bouillon dissolves, about 10 minutes. Ladle about 1/4 cup hot broth into a bowl; whisk 2 tablespoons cornstarch into bowl until dissolved. Stir cornstarch mixture into the broth mixture in the pot. Cook, stirring occasionally, until mixture thickens, about 5 minutes.
Stir beef and onion mixture and any accumulated pan juices into broth mixture; cook until heated through, 2 to 3 minutes.
