Bring a large pot of salted water to a boil and cook the pasta until just al dente, about 1 minute less than package instructions. Drain and set aside.
Drain and rinse the soaked cashews, then add them to a blender along with garlic, nutritional yeast, lemon juice, plant-based milk, and a pinch of salt. Blend on high until the mixture is smooth and creamy, stopping to scrape down the sides as needed.
Pour the creamy sauce into a large mixing bowl, then fold in the cooked pasta, chopped spinach, and sautéed mushrooms. Sprinkle smoked paprika, salt, and pepper over the mixture and toss well to combine, ensuring everything is evenly coated.
Transfer the mixture into a greased baking dish, spreading it out evenly with a spatula. Sprinkle vegan cheese or breadcrumbs on top for a crispy, cheesy crust.
Bake in a preheated oven at 180°C (356°F) for 25–30 minutes, until bubbling around the edges and the top is golden brown.
Remove from the oven and let the pasta bake rest for 5 minutes. This helps the sauce set slightly and makes serving easier.
Slice into portions, serve hot, and enjoy the cheesy, creamy goodness with a sprinkle of fresh herbs if desired.