Even though they have greenish flesh and not as sweet as most fruits, avocados are bona fide tree-fruits. As such, the blessing on avocado is “Ha’etz:”

בָּרוּךְ אַתָּה יְ‑יָ אֱ‑לֹהֵינוּ מֶלֶךְ הָעוֹלָם בּוֹרֵא פְּרִי הָעֵץ

Bah-rookh ah-tah ah-doh-noy, eh-loh-hay-noo meh-lehkh hah-oh-lahm boh-ray peh-ree hah-aytz

Blessed are You, L‑rd our G‑d, King of the universe, Who creates the fruit of the tree

The after-blessing for avocado is Borei Nefashot.