Heat oil in a large skillet over medium-high heat. Brown beef in a single layer, 2-3 minutes per side. Work in batches if needed. Set aside.
Pour water into the crockpot and stir in both seasoning packets until dissolved. Add the browned beef and scrape the skillet's browned bits into the pot.
Add onion, tomatoes with juice, tomato sauce, carrots, potatoes, and green beans. Stir to submerge vegetables in broth.
Add corn last. Cover and cook on low for 6-8 hours until beef is fork-tender and potatoes break apart easily.
Taste and adjust salt if needed. Ladle into bowls and serve hot.