Preheat the oven to 325°F (163°C) and line a rimmed baking sheet with parchment paper or lightly grease it.
In a mixing bowl, beat the softened cream cheese with a hand-held electric mixer until smooth.
Add the Buffalo wing sauce, 1/3 cup blue cheese dressing, and 1/2 teaspoon garlic powder to the cream cheese and beat until fully combined and smooth.
Fold in the finely diced cooked chicken, shredded cheddar, and sliced green onions until evenly distributed.
Slice each jalapeño in half lengthwise and use a small spoon to scoop out the seeds and membranes; wear gloves if desired.
Spoon the buffalo chicken mixture into each jalapeño half, dividing it evenly among the 15 halves.
Arrange the stuffed jalapeño halves on the prepared baking sheet, spacing them slightly apart.
Bake for 30 minutes, or until the filling is heated through and the tops are lightly golden.
Serve warm with extra blue cheese dressing for dipping.