In food processor, pulse together garlic, avocados, spinach, nutritional yeast, dill, oil, water, lemon zest, lemon juice, salt and pepper until smooth. Mixture will resemble pesto. Set aside.
In large saucepan of boiling salted water, cook pasta according to package instructions. Add asparagus during last 4 minutes of cooking.
Reserving ¼ cup of the cooking liquid, drain pasta and asparagus. Return to pan; gently stir in pesto until combined.
If needed, gradually stir in enough of the reserved cooking liquid to loosen sauce.
Garnish with sprigs of fresh dill and sprinkle with more nutritional yeast, if you wish.
