Heat olive oil in a large pot over medium-high heat. Brown beef in batches, about 4–5 minutes. Remove and set aside.
Add onion, carrots, and celery to the pot, cooking 6–7 minutes until softened.
Add mushrooms and cook 8–10 minutes, until they release their liquid and begin to brown.
Return beef to the pot and pour in broth.
Simmer, covered, 25–30 minutes, until beef is tender.
Stir in cauliflower rice and simmer 5 more minutes, until just tender.
Season with salt and pepper, garnish with parsley, and serve.