Bring a large pot of well-salted water to a boil. Cook pasta until al dente according to package directions. Before draining, scoop out at least 1/2 cup of pasta water. Drain the pasta and return to the warm pot.
Add avocado flesh, garlic, basil, lemon juice, lemon zest, olive oil, salt, pepper, and red pepper flakes to a blender or food processor. Add 1/4 cup hot pasta water and blend on high until completely smooth. Add more pasta water a tablespoon at a time if too thick. Taste and adjust seasoning.
Pour avocado sauce over hot drained pasta immediately. Toss quickly with tongs until every strand is evenly coated. Add a splash more pasta water if the sauce feels too thick as you toss.
Divide into bowls. Add a squeeze of lemon juice, grated parmesan or nutritional yeast, fresh basil, cherry tomatoes if using, red pepper flakes, and cracked black pepper. Serve immediately.
