In a medium saucepan, heat the vegetable broth and keep it warm over low heat.
In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté until softened, about 3-4 minutes.
Stir in the minced garlic and sliced mushrooms. Cook for an additional 5-7 minutes, or until the mushrooms are tender and begin to brown.
Add the orzo to the skillet with the mushrooms, stirring to combine. Toast the orzo lightly for 2-3 minutes.
Gradually pour in the warm vegetable broth, one ladle at a time, stirring continuously. Allow the orzo to absorb the broth before adding more, about 15-20 minutes total.
Once the orzo is cooked and creamy, reduce the heat to low and stir in the heavy cream, grated Parmesan cheese, thyme, salt, and pepper. Mix until everything is well combined and heated through.
Adjust seasoning to taste and remove from heat.
Notes
Serve in shallow bowls, garnished with parsley and extra Parmesan.