Preheat the oven to 375 degrees F. Line a baking sheet with parchment paper and set aside.
Mix the shredded chicken, shredded cheese, sour cream, 1/4 cup salsa verde, and green onions in a bowl. Lay the tortillas out and spread 2 tablespoons of refried beans across each tortilla. Top with 2 tablespoons of chicken mixture.
To roll: fold one side of the tortilla over the fillings and pull back to make the filling tightly packed. Fold the short ends inward and roll to secure the short ends. Fold the short ends in again, if needed and roll to the end. Place the chimichangas on the prepared baking sheet.
Brush the chimichangas completely with melted butter, or thoroughly coat with cooking spray. Bake for 10-12 minutes until golden.
Meanwhile, place 3/4 cup of salsa verde in the blender with the flesh of one ripe avocado. Puree until smooth.
To serve: Serve the chimichangas fresh out of the oven with a side of the creamy avocado salsa verde, or top each chimichanga with salsa verde and any other topping you like!