Heat olive oil in a large deep skillet or pot over medium heat.
Add the chopped onion and cook for 3-4 minutes until translucent.
Add the sliced mushrooms and cook for 6-7 minutes, stirring occasionally, until they release their moisture and start to brown.
Add the minced garlic and cook for 1 minute until fragrant.
Add the broken fettuccine pasta to the pot and stir to combine with the mushrooms and onions.
Pour in the vegetable broth and bring the mixture to a boil.
Reduce heat to medium-low and simmer uncovered, stirring occasionally, for about 12 minutes or until the pasta is tender and most of the liquid is absorbed.
Stir in the heavy cream, grated Parmesan cheese, salt, black pepper, and dried thyme.
Cook for another 2-3 minutes, stirring frequently, until the sauce thickens and becomes creamy.
Remove from heat and sprinkle with chopped fresh parsley before serving.