Heat olive oil in a saucepan over medium heat. Add onion and cook until soft, about 3 minutes. Add garlic and cook for 1 minute more. Add cauliflower and vegetable broth; cover with lid and simmer over medium heat until tender, about 5 minutes.
Place cauliflower mixture in a blender. Add nutritional yeast, salt, lemon juice, and soy sauce; blend until smooth and creamy, about 3 minutes.