Pasta and Vegetables:
To make the pasta and vegetables, cook pasta according to the package instructions. Drain and return to the pot. Meanwhile, bring 1/2 cup water to a boil in a small saucepan. Add broccoli and a pinch of salt and pepper. Cover and cook 1 to 2 minutes, until just tender.
Drain broccoli and add to pasta pot. Heat oil in a skillet over medium heat. Add mushrooms with a pinch of salt and pepper and cook until lightly browned, stirring occasionally for about 2 minutes. Add mushrooms to pasta and broccoli.
To make the Alfredo sauce, drain the soaked cashews. Put cashews in a food processor with 3/4 cup of the rice milk. Process until well combined and smooth, scraping down sides of the bowl as needed. Add remaining 1/4 cup rice milk and continue processing until very smooth. Pour cashew mixture into a small saucepan over medium-low heat. Add nutritional yeast, miso, salt and pepper and whisk until well blended and warm. Taste and adjust seasoning, adding mustard and/or lemon juice if a tangier flavor is desired.
Pour Alfredo sauce over pasta and vegetables and toss gently to combine. Divide between two bowls and garnish with red pepper flakes and basil, if using. Serve immediately.