Preheat your oven to 425°F and line a baking sheet with parchment paper.
Steam the cauliflower florets until tender (about 6-8 minutes), then transfer to a food processor and pulse until rice-like texture is achieved.
Place the riced cauliflower in a microwave-safe bowl and microwave for 3 minutes. Let cool slightly and then place in a clean kitchen towel. Squeeze out as much moisture as possible.
In a bowl, combine the dried cauliflower, egg, garlic powder, salt, and pepper until a dough forms. Press the mixture firmly onto the prepared baking sheet to form a thin, even crust.
Bake the crust in the oven for 12-15 minutes, or until it begins to turn light golden.
While the crust bakes, season the chicken breast with salt and pepper. Cook the chicken in a skillet over medium heat until fully cooked and lightly browned on both sides (about 5-6 minutes per side). Let cool, then shred or dice the chicken.
Toss the shredded chicken with buffalo sauce until well coated.
Spread the buffalo chicken evenly over the pre-baked crust, then sprinkle the shredded mozzarella cheese on top.
Return the pizza to the oven and bake for an additional 8-10 minutes, or until the cheese is melted and bubbly.
Garnish with chopped green onions before serving.