Thanks to the inexpensive Raspberry Pi Zero, Internet of Things (IoT) projects will continue to grow. One disadvantage which the Zero (not W) and A+ models have is the lack of Ethernet connectivity. That would not be a problem, if not just a single (micro) USB port onboard.
In order to connect these models with the network by Ethernet cable without a WLAN adapter, one can do this over the GPIOs: All you need is the “ENC28J60” module, the connection of which is shown in this tutorial.
Source: Raspberry Pi Zero – Establishing an Ethernet connection (ENC28J60) (Raspberry Pi Tutorials)