Heat oven to 400°F. Line a large baking sheet with parchment.
Arrange jalapeño halves cut-side up on the sheet. Pat dry to remove moisture.
Beat cream cheese with buffalo sauce, garlic powder, onion powder, salt, and pepper until smooth.
Fold in shredded chicken, cheddar, and green onions until evenly combined.
Stir panko with melted butter in a small bowl to coat; set aside.
Spoon the filling into jalapeños, mounding slightly. Sprinkle with buttery panko if using.
Bake 18–20 minutes until peppers soften and filling bubbles. Broil 1–2 minutes to brown tops.
Rest 5 minutes. Garnish with parsley and serve warm with ranch or blue cheese dressing.