Put the avocado, basil, oil, garlic, and a generous amount of salt and pepper into a food processor and blend until smooth.
Cook the pasta in a pan of boiling salted water for a minute less than the package directions, drain, then return to the pan with sauce and gently heat through over low heat for 1 minute. Divide between 2 bowls and serve topped with basil leaves and a little more black pepper, if you like.