Combine the chicken, onion, mayonnaise, chili powder, salt and pepper in a NutriBullet or other high-powered blender until it reaches a creamy consistency.
Wearing gloves, fill each jalapeño half with a spoonful of chicken mixture. It should be slightly heaping without spilling over.
Wrap each jalapeño half with a slice of bacon. Fold the bacon underneath the pepper so it stays put.
Bake for about 20 minutes or until you can smell the peppers begin to roast. (You'll know it when you smell it.)