Cook pasta as directed on package. Drain well.
Meanwhile, cook bacon in large skillet on medium-high heat until crisp. Remove bacon. Drain on paper towels; crumble bacon. Set aside. Add 2 cups of the kale to drippings in skillet; cook and stir 1 to 2 minutes or just until kale is tender-crisp. Remove kale. Set aside. Add onion to skillet; cook and stir 2 minutes. (Add oil if needed.) Add chicken stock and seasonings; bring to boil. Reduce heat to low; simmer 5 minutes.
Place remaining 4 cups kale in blender container. Add avocado, pistachios, 2 tablespoons of the Parmesan cheese and 1/2 of the crumbled bacon. Add hot stock mixture. Cover blender with lid with center part removed. Cover lid with towel. Blend on low speed 15 seconds. Blend on high speed until mixture is smooth.
Place pasta in serving bowl. Top with kale sauce, cooked kale, remaining crumbled bacon and remaining 2 tablespoons Parmesan cheese. Sprinkle with additional chopped pistachios, if desired.