Heat the olive oil in a large, deep skillet or Dutch oven over medium heat.
Add the sliced mushrooms and cook until they release their liquid and brown, about 8 minutes.
Add the chopped onion and minced garlic to the skillet. Cook until the onion softens, about 3 minutes.
Stir in the orzo pasta and dried thyme. Cook for 1 minute, stirring constantly.
Pour in the vegetable broth. Bring the mixture to a boil, then reduce the heat to low, cover, and simmer for 12 to 15 minutes, or until the orzo is tender and most of the liquid is absorbed. Stir occasionally to prevent sticking.
Remove the pot from the heat. Stir in the heavy cream and grated Parmesan cheese until the sauce is smooth and creamy.
Season with salt and pepper to your taste.
Serve immediately, garnished with fresh parsley.
Notes
If the orzo seems too thick before it is fully cooked, add a splash more broth or water.
You can substitute half-and-half for heavy cream for a slightly lighter texture.
Use fresh mushrooms for the best flavor in this one pot orzo dinner.