Combine the water, potato, carrots, garlic, onion, chiles, tomato, and cashews in a skillet over medium-high heat. Cover and cook for 18 to 20 minutes or until the cubed potato is tender. Allow the mixture to cool slightly.
Cook the elbow pasta according to package instructions. In the last 2 minutes of boiling, add the chopped broccoli. Drain the pasta and broccoli and set aside.
Pour the vegetable mixture, mustard, soy sauce, nutritional yeast, lemon juice, olive oil, paprika, and sriracha into a blender. Blend for 1 minute, allow it to rest for 1 minute, then blend again until smooth.
Transfer the vegan mac and cheese sauce to a saucepan over medium heat. Stir in the salt and pepper. If the sauce is too thick, add more water to adjust its consistency.
Bring the vegan cheese sauce almost to a boil. Taste and season as needed.
Add the cooked pasta and broccoli to the sauce. Mix well to coat everything. Cover and cook for 3 minutes.
Let the mac and cheese sit for 2 minutes, and sprinkle the remaining pepper over the pasta. Enjoy!