Cook the fettuccine according to package instructions until al dente. Drain and set aside, reserving 1/2 cup of the pasta water.
In a blender, combine the soaked cashews, vegetable broth, and a pinch of salt. Blend until smooth and creamy. Set aside.
In a large skillet, heat the olive oil over medium heat. Add the diced onion and sauté for about 5 minutes until translucent.
Add the minced garlic and sliced mushrooms to the skillet. Cook for another 5-7 minutes, stirring occasionally, until the mushrooms are tender and browned.
Stir in the dried thyme, dried oregano, salt, and pepper. Mix well to combine.
Pour the cashew cream sauce into the skillet with the mushrooms and stir to combine. If the sauce is too thick, add some reserved pasta water to reach desired consistency.
Add the cooked fettuccine to the skillet and toss to coat the pasta evenly with the sauce. Cook for an additional 2-3 minutes to heat through.
Serve immediately, garnished with fresh parsley and lemon wedges on the side.