01 - Prepare pasta according to package directions until al dente. Drain thoroughly, reserving ½ cup of the cooking liquid, and set aside.
02 - Combine soaked cashews, sun-dried tomatoes, plant-based milk, nutritional yeast, garlic, lemon juice, oregano, salt, and black pepper in a high-speed blender. Process until completely smooth and creamy, approximately 1-2 minutes.
03 - Heat olive oil (or reserved sun-dried tomato oil) in a large skillet over medium heat. Add finely chopped onion and cook for 3-4 minutes until translucent and fragrant.
04 - Pour the blended sun-dried tomato sauce into the skillet with the onions. Bring to a gentle simmer and cook for 3-4 minutes, stirring occasionally to prevent sticking.
05 - Stir in fresh baby spinach and cook until just wilted, approximately 2 minutes. The spinach should remain vibrant green.
06 - Add cooked pasta to the skillet and toss thoroughly to coat with sauce. Add a splash of reserved pasta water if the sauce appears too thick. Serve immediately, garnished with torn fresh basil leaves and red pepper flakes if desired.