Season beef with salt. Heat oil in a large saucepan over medium-high heat. Sauté beef in batches until browned.
Return meat to pan and reduce heat to medium. Add garlic, onion, and celery. Cook until soft, about 5 minutes. Add flour and thyme, and cook for 2 more minutes. Stir in broth and bay leaves, bring to a simmer, and cook covered until beef is tender, 30 to 40 minutes. Add frozen veggies and cook for 10 minutes, until heated through.
Bake tater tots per package directions. Ladle soup into bowls and top each with tots.