In a food processor, pulse the sunflower seeds and nutritional yeast until finely chopped. Add the arugula and pulse until chopped. Add the lemon juice and garlic, and pulse until combined. Slowly drizzle in the olive oil with the machine running until incorporated. Stop to scrape down the sides as needed.
Cook the pasta according to the package directions. When the pasta has one minute remaining, add the asparagus and yellow pepper to blanch them.
While pasta is cooking, melt the buttery spread in a pan over medium heat. Stir in the flour and cook, while whisking, for 1 minute. While whisking, pour in about ⅓ of the milk beverage, and continue whisking until incorporated. Repeat twice, with the remaining ⅔ of the milk beverage. Stir in the salt and pesto.
Toss the sauce with the hot pasta, vegetables, and cherry tomatoes. Season to taste, if needed.