Make the Cashew Cream: Add the soaked cashews to a high-speed blender along with the tomato paste, salt, and water. Blend on high for 30-45 seconds, until smooth. Set aside.
Cook the Pasta: Bring a large pot of generously salted water to a boil. Add the pasta and cook until al dente, according to the package instructions. Once the pasta water begins to foam, reserve 1 cup of the pasta water and set aside. Drain the pasta once cooked, but do not rinse.
Sauté: Warm the oil in a large pan over medium heat. Add the red pepper flakes (if using) and capers and sauté for 1 to 2 minutes, until sizzling. Add the mushrooms to the pan and sauté for 5 to 7 minutes, stirring occasionally, until they have darkened and released most of their liquid.
Add Seasonings: Add the sun-dried tomatoes, garlic and basil to the pan and sauté for 2 minutes, until the garlic is fragrant.
Make it Saucy: Add the chickpeas the the blended cashew cream sauce to the pan and mix well. Bring the mixture to a simmer, then add in 1/2 cup (120 ml) of the reserved pasta water and stir well. Bring to a simmer and cook for 5 minutes, stirring occasionally.
Final Touches: Add the spinach and drained pasta to the sauce and mix well, cooking until the spinach has wilted. If the sauce is to thick for your liking you can thin it out with the additional reserved pasta water.
Serve & Store: Serve warm, topped with fresh basil or as desired. Leftovers will keep in the fridge for up to 5 days.