Preheat your oven to 400 degrees.
Arrange your halved bell peppers in a lightly greased large skillet or baking dish, cut side up.
In a large bowl, combine pre-cooked shredded chicken, mayonnaise, hot sauce, garlic powder, onion powder, salt, black pepper, nutritional yeast (if using), and green onions. Mix everything until well combined.
Generously fill each prepared pepper with your buffalo chicken mixture, packing it in tightly.
Cover your baking dish with foil and bake stuffed peppers for about 30 minutes. Then remove the foil and bake for another 20 minutes until the peppers are tender and the filling is bubbling and slightly browned.
Top your stuffed peppers with a drizzle of Whole30 ranch dressing, sprinkle some thinly sliced green onion on top along with fresh herbs if desired. Serve them warm.