Bring a large pot of salted water to a boil and cook the red lentil pasta according to package directions until al dente.
While the pasta cooks, place the silken tofu, raw cashews, nutritional yeast, lemon juice, and vegetable broth into a high-speed blender.
Blend the sauce ingredients until completely smooth and creamy, then set aside.
Heat a large non-stick skillet over medium-high heat and add the diced onions and sliced mushrooms.
Sauté the vegetables for 6-8 minutes until the mushrooms are browned and the onions are translucent, adding a splash of water if they begin to stick.
Add the minced garlic to the skillet and cook for an additional 1 minute until fragrant.
Drain the pasta, reserving a small amount of pasta water, and return the pasta to the pot.
Pour the cashew-tofu cream sauce and the sautéed mushroom mixture over the pasta.
Toss everything together over low heat for 2 minutes until the sauce thickens and coats the pasta, adding reserved water if needed.
Season with sea salt and black pepper before serving immediately.