Preheat oven to 450°F. Grease a baking sheet with cooking spray.
In a large bowl, whisk flour, water, garlic powder and paprika in a bowl until batter is smooth. Add cauliflower to batter and toss to coat.
Spread cauliflower onto the baking sheet in a single layer, season with salt and pepper. Bake in the preheated oven until lightly browned, 20 to 25 minutes, flipping over halfway through for even baking.
In another small bowl, whisk hot sauce, melted butter and lemon juice until well combined. Brush the buffalo sauce mixture on the cauliflower.
Return to the oven and bake until they start to brown, about 15 minutes.
Serve hot with ranch dressing, celery and carrots, if desired