Stir in onions and garlic for 2 minutes or so. Then stir in the carrots. Add soy sauce, water, oyster sauce, Worcestershire sauce, and black pepper. Stir everything together. Cover to soften the carrots.
Stir in the cauliflower florets and celery. Adding them in the end will keep their texture. Cook for a few minutes. Stir the cornstarch mixture to thicken the sauce.