Preheat oven to 375°F (190°C).
Remove the stems from the mushrooms and carefully scoop out some of the insides to create space for the filling.
In a bowl, mix the shredded chicken, buffalo sauce, cream cheese, cheddar cheese, ranch dressing, green onions, and a pinch of salt and pepper.
Spoon the chicken mixture into each mushroom cap, pressing gently to pack it in.
Arrange the stuffed mushrooms on a baking sheet and drizzle with olive oil.
Bake for 15-20 minutes, or until the mushrooms are tender and the filling is bubbly.
Serve warm, garnished with additional green onions or ranch for dipping.