Heat 1 tablespoon olive oil in a medium skillet pan over medium heat. Add the onion and cook for 3-4 minutes, stirring occasionally.
Add the ground beef, sprinkle with 1 teaspoon salt, and cook until browned and no longer pink. Drain any excess grease.
To a 6-quart slow cooker, add the cooked onion and ground beef, celery, carrots, bell pepper, potatoes, tomato paste, garlic powder, Italian seasoning, 2 teaspoons salt, pepper, chicken stock, and water, stirring until well combined.
Cover and cook on high for 4-5 hours or low for 7-8 hours, or until the vegetables are tender and cooked through.
Uncover and add the red wine vinegar, stirring to combine. Taste and add additional salt, vinegar or pepper to taste. Serve with toppings of your choice.
