In a large skillet, bring about ¼” water to boil. Add cauliflower, cover pan, and steam until tender, about 4 minutes. Drain and let cool while you prep other ingredients.
In a large skillet over medium heat, cook bacon until crispy, about 3 minutes per side. Transfer to a paper towel-lined plate to drain, then chop.
In a large bowl, whisk together sour cream, mayonnaise, lemon juice, and garlic powder. Add cauliflower and toss gently. Season with salt and pepper, then fold in bacon, cheddar, and chives. Serve warm or at room temperature.