Bring a large pot of salted water to a boil and cook the pasta according to the package directions until al dente. Reserve about 1 cup of the pasta water, then drain the pasta.

While the pasta cooks, heat the olive oil in a large skillet over medium heat. Add the onion and cook for 4 to 5 minutes, stirring occasionally, until softened.

Add the garlic and cook for 30 seconds, then stir in the chopped sun-dried tomatoes and cook for 1 minute more.

In a blender, combine the soaked cashews, plant-based milk, vegetable broth, nutritional yeast, lemon juice, dried basil, oregano, salt, black pepper, and red pepper flakes if using. Blend until completely smooth and creamy.

Pour the sauce into the skillet with the onion and sun-dried tomato mixture. Stir and simmer over medium-low heat for 3 to 5 minutes, until slightly thickened.

Add the cooked pasta to the skillet and toss to coat. If the sauce is too thick, add reserved pasta water a little at a time until it reaches your desired consistency.

Stir in the baby spinach if using and cook just until wilted. Taste and adjust seasoning with more salt or pepper if needed.

Serve hot, topped with fresh basil.