You can use any type of mushrooms, not just shiitake.
For an extra umami kick, try sprinkling over togarashi (spicy!) or furikake, both Japanese seasonings with seaweed, sesame seeds and other flavored goodness.
Orzo pasta is not a must; other small pasta shapes can be used to achieve a creamy risotto-like feel.
Whisk until silky and creamy, applying some elbow grease. If it needs thinning, add more pasta water until you get the desired consistency.