Preheat oven to 400°F.
In a large bowl, toss 8 cups cauliflower florets with 2 tablespoons olive oil and 1 teaspoon of the salt until evenly coated. Spread the cauliflower in a single layer on a baking sheet.
Roast the cauliflower 15–25 minutes, stirring once halfway through, until fork-tender and golden brown. Remove from the oven.
Place a large skillet over medium heat. Add 1 cup buffalo sauce and 8 ounces cream cheese (in cubes) to the skillet and whisk or stir until the cream cheese is fully melted and the sauce is smooth.
Add the roasted cauliflower to the skillet, increase heat to medium-high, and bring the mixture to a simmer. Stir frequently and simmer until the sauce begins to thicken, about 4–6 minutes.
Remove the skillet from the heat. Gradually add 6 ounces grated cheddar, stirring after each addition and waiting until the cheese melts before adding more.
Stir in 3/4 cup low-fat sour cream or 2% Greek yogurt and the remaining 1 teaspoon salt until fully combined.
Transfer the mixture to a cast-iron pan or other oven-safe baking dish and spread evenly.
Bake in the 400°F oven until bubbly, about 10–15 minutes.
Remove from the oven and garnish with sliced green onions before serving.