Bring a large pot of salted water to a boil. Add spaghetti or linguine and cook according to package instructions until al dente (about 8 minutes).

In a blender, combine avocados, garlic, lemon juice, olive oil, salt, and pepper. Blend until smooth.

Fold in the chopped basil by pulsing gently in the blender.

Drain the pasta (do not rinse) and return it to the pot over low heat. Pour in the avocado sauce and toss until well coated.

Plate immediately, garnishing with extra basil or red pepper flakes if desired.