Add chicken broth, onion soup, water, tomato paste, and soy sauce into bowl of slow cooker. Whisk to breakup and distribute tomato paste.
In a large bowl, season beef with salt and pepper. Mix to combine.
Add seasoned beef, potatoes, onion, and carrots to slow cooker. Cover with lid and cook on high for 6-7 hours until the beef is tender.
Before serving, add frozen peas and allow to cook for 5-8 minutes. Stir in 1/4 cup potato flakes to thicken soup. Add additional potato flakes 1 tablespoon at a time to achieve desired thickness. Season with additional salt and pepper to taste. Serve with toasted crusty bread.