Cut up the cauliflower, stems included, into small pieces and place in a large colander. Rinse thoroughly under running water and let drain briefly when finished. Place cauliflower in a large, microwave-safe dish with garlic, the white part of the green onions, and the dried parsley. Add 2-3 tablespoons of water and season with pepper, to taste. Cover container and microwave on high until the cauliflower is fork tender, approximately 6-7 minutes. (Actual cooking time will vary depending on microwave strength and the amount of cauliflower used, so test after 4 minutes and adjust cooking time accordingly). Remove from microwave, and fill blender container nearly half full with the steamed cauliflower mixture. Add 1 cup stock to the blender and blend until smooth.
(Make sure the blender lid is adequately vented to allow steam to escape before turning on the blender). Pour cauliflower puree into a large soup pot and repeat with the remaining steamed cauliflower mixture and stock until it has all been pureed and transferred to the pot. Turn heat to medium and cook until the cauliflower mixture is heated through, about 5-6 minutes, while stirring occasionally. Add the goat cheese and stir until blended. Cook another minute or two, or until the soup is uniformly heated. If soup is too thick, add additional stock to reach the desired consistency. If it is too thin, continue cooking until excess moisture has been reduced. Taste and season with additional pepper, if desired. Serve immediately topped with sliced green onion.