Place the chocolate chips in a small microwave-safe bowl. Microwave for 1 minute 30 seconds on 50% power. Stir and then microwave in 30 second intervals at 50% power, stirring in between, until completely smooth and melted. Set aside to cool.
Meanwhile, in a large bowl with an electric mixer, beat the cream cheese, butter, brown sugar, and granulated sugar until creamy. Add the eggs and vanilla and beat well. Add the melted, slightly cooled chocolate and mix again until well combined.
In a separate medium bowl, use a spoon to combine the oats, flour, nuts, baking soda, and salt. Add the dry mixture to the chocolate mixture and stir with a spoon until well combined. Cover and chill for at least 1 hour or longer.
Heat oven to 350 degrees F and line a baking sheet with parchment paper.
Shape the chilled dough into 1 ½ inch balls and place them a couple of inches apart on the prepared baking sheet.
Bake 10 to 12 minutes or until cracks begin to form on the surface and cookies are almost set but still soft on top. Baking time can vary depending on the temperature of the dough and size of the cookies. Cool for 1 to 2 minutes on the baking sheet and then transfer to wire a rack to cool completely.
Once cooled, sprinkle the tops with powdered sugar.
Store the completely cooled cookies in an airtight container.