Preheat oven to 450°F. Coat a large rimmed baking sheet with cooking spray.
Toss cauliflower, oil and salt in a large bowl. Spread on the prepared baking sheet; reserve the bowl. Roast the cauliflower until it’s starting to soften and brown on the bottom, about 15 minutes.
Meanwhile, combine Buffalo sauce, butter and lemon juice in the large bowl. Add the roasted cauliflower and toss to coat. Return the cauliflower to the baking sheet and continue roasting until hot, about 5 minutes more.